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Found 11 results

  1. Here we go with a fresh model discussion thread - things are getting very interesting right now! Want to have a bit of banter or a ramp and moan only loosely related to the models? The banter thread is for you: https://www.netweather.tv/forum/topic/86721-model-moans-ramps-and-banter/ Want to talk about the snow / cold weather in your part of the country? The regional threads are the place for you: https://www.netweather.tv/forum/forum/142-regional-discussions/ Want to view the model outputs? You can get all the major ones here on Netweather: GFS GEFS Ensembles ECMWF ECMWF EPS NetWx-SR NetWx-MR Met-Office Fax GEM GFS Hourly Snow forecast and precip type Model Comparison Global Jet Stream Stratosphere Happy model watching
  2. Here we go then, already plenty of interest in the strat this year, and with a La Nina likely, perhaps a less hardcore strat than last year can be expected? @chionomaniac will be along soon to fill in his thoughts on where things may be headed this year, but in the meantime, I've copied his excellent strat guide from 2015 below. For more info you can also read his full tutorial here: https://www.netweather.tv/charts-and-data/stratosphere/tutorial Ed's opener from 2015/16 As ever, the first post will become both a reference thread and basic learning thread for those wanting to understand how the stratosphere may affect the winter tropospheric pattern, so forgive me for some repeat from previous years, but it is important that those new to the stratosphere have a place that they can be directed to in order to achieve a basic grasp of the subject. The stratosphere is the layer of the atmosphere situated between 10km and 50km above the earth. It is situated directly above the troposphere, the first layer of the atmosphere and the layer that is directly responsible for the weather that we receive at the surface. The boundary between the stratosphere and the troposphere is known as the tropopause. The air pressure ranges from around 100hPa at the lower levels of the stratosphere to below 1hPa at the upper levels. The middle stratosphere is often considered to be around the 10-30hPa level. Every winter the stratosphere cools down dramatically as less solar UV radiation is absorbed by the ozone content in the stratosphere. The increasing difference in the temperature between the North Pole and the latitudes further south creates a strong vortex – the wintertime stratospheric polar vortex. The colder the polar stratosphere in relation to that at mid latitudes, the stronger this vortex becomes. The stratospheric vortex has a strong relationship with the tropospheric vortex below. A strong stratospheric vortex will lead to a strong tropospheric vortex. This relationship is interdependent; conditions in the stratosphere will influence the troposphere whilst tropospheric atmospheric and wave conditions will influence the stratospheric state. At the surface the strength and position of the tropospheric vortex influences the type of weather that we are likely to experience. A strong polar vortex is more likely to herald a positive AO with the resultant jet stream track bringing warmer and wet southwesterly winds. A weaker polar vortex can contribute to a negative AO with the resultant mild wet weather tracking further south and a more blocked pattern the result. A negative AO will lead to a greater chance of colder air spreading to latitudes further south such as the UK. AO chart The stratosphere is a far more stable environment then the troposphere below it. However, the state of the stratosphere can be influenced by numerous factors – the current solar state, the Quasi Biennial Oscillation (QBO), the ozone content and distribution and transport mechanism, the snow cover and extent indices and the ENSO state to name the most significant. These factors can influence whether large tropospheric waves that can be deflected into the stratosphere can disrupt the stratospheric polar vortex to such an extent that it feeds back into the troposphere. Ozone Content in the stratosphere Ozone is important because it absorbs UV radiation in a process that warms the stratosphere. The Ozone is formed in the tropical stratosphere and transported to the polar stratosphere by a system known as the Brewer-Dobson-Circulation (the BDC). The strength of this circulation varies from year to year and can in turn be dictated by other influences. The ozone content in the polar stratosphere has been shown to be destroyed by CFC's permeating to the stratosphere from the troposphere. The overall ozone content in the polar stratosphere will help determine the underlying polar stratospheric temperature, with higher contents of ozone leading to a warmer polar stratosphere. The ozone levels can be monitored here: http://www.cpc.ncep.noaa.gov/products/stratosphere/sbuv2to/index.shtml One of the main influences on the stratospheric state is the QBO. This is a tropical stratospheric wind that descends in an easterly then westerly direction over a period of around 28 months. This can have a direct influence on the strength of the polar vortex in itself. The easterly (negative) phase is thought to contribute to a weakening of the stratospheric polar vortex, whilst a westerly (positive) phase is thought to increase the strength of the stratospheric vortex. However, in reality the exact timing and positioning of the QBO is not precise and the timing of the descending wave can be critical throughout the winter. Diagram of the descending phases of the QBO: (with thanks from http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo/index.html ) The QBO has been shown to influence the strength of the BDC, depending upon what phase it is in. The tropical upward momentum of ozone is stronger in the eQBO , whereas in the wQBO ozone transport is stronger into the lower mid latitudes, so less ozone will enter the upper tropical stratosphere to be transported to the polar stratosphere as can be seen in the following diagram. http://www.atmos-chem-phys.net/13/4563/2013/acp-13-4563-2013.pdf However, the direction of the QBO when combined with the level of solar flux has also been shown to influence the BDC. When the QBO is in a west phase during solar maximum there are more warming events in the stratosphere, as there is also during an easterly phase QBO during solar minimum, so the strength of the BDC is also affected by this – also known as the Holton Tan effect . http://strat-www.met.fu-berlin.de/labitzke/moreqbo/MZ-Labitzke-et-al-2006.pdf http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50424/abstract http://onlinelibrary.wiley.com/doi/10.1002/2013JD021352/abstract The QBO is measured at 30 hPa and has entered a westerly phase for this winter. As mentioned warming events are more likely during solar maximum when in this westerly phase – with the solar flux below 110 units. Currently, we have just experienced a weak solar maximum and the solar flux heading into winter is still around this mark. This doesn’t rule out warming events, but they will not be as likely – perhaps if the solar flux surges then the chance will increase. Latest solar flux F10.7cm: http://www.swpc.noaa.gov/products/solar-cycle-progression Sudden Stratospheric Warmings: One warming event that can occur in the stratospheric winter is a Sudden Stratospheric Warming (SSW) or also known as a Major Midwinter Warming (MMW). This, as the name suggests is a rather dramatic event. Normally the polar night jet at the boundary of the polar vortex demarcates the boundary between warmer mid latitude and colder polar stratospheric air (and ozone levels) and this is very difficult to penetrate. SSWs can be caused by large-scale planetary tropospheric (Rossby) waves being deflected up into the stratosphere and towards the North Pole, often after a strong mountain torque event. These waves can introduce warmer temperatures into the polar stratosphere which can seriously disrupt the stratospheric vortex, leading to a slowing or even reversal of the vortex. Any SSW will be triggered by the preceding tropospheric pattern - in fact the preceding troposheric pattern is important in disturbing the stratospheric vortex even without creating a SSW. Consider a tropospheric pattern where the flow is very zonal - rather like the positive AO phase in the diagram above. There has to be a mechanism to achieve a more negative AO or meridional pattern from this scenario and there is but it is not straightforward. It just doesn't occur without some type of driving mechanism. Yes, we need to look at the stratosphere - but if the stratosphere is already cold and a strong polar vortex established, then we need to look back into the troposphere. In some years the stratosphere will be more receptive to tropospheric interactions than others but we will still need a kickstart from the troposphere to feedback into the stratosphere. This kickstart will often come from the tropics in the form of pulses and patterns of convection. These can help determine the position and amplitude of the long wave undulations Rossby waves - that are formed at the barrier between the tropospheric polar and Ferrel cells. The exact positioning of the Rossby waves will be influenced by (amongst other things) the pulses of tropical convection, such as the phase of the Madden Jullian Oscillation and the background ENSO state and that is why we monitor that so closely. These waves will interact with land masses and mountain ranges which can absorb or deflect the Rossby waves disrupting the wave pattern further - and this interaction and feedback between the tropical and polar systems is the basis of how the Global Wind Oscillation influences the global patterns. If the deflection of the Rossby Wave then a wave breaking event occurs – similar to a wave breaking on a beach – except this time the break is of atmospheric air masses. Rossby wave breaks that are directed poleward can have a greater influence on the stratosphere. The Rossby wave breaks in the troposphere can be demonstrated by this diagram below – RWB diagram: https://www.jstage.jst.go.jp/article/jmsj/86/5/86_5_613/_pdf This occurs a number of times during a typical winter and is more pronounced in the Northern Hemisphere due to the greater land mass area. Most wave deflections into the stratosphere do change the stratospheric vortex flow pattern - this will be greater if the stratosphere is more receptive to these wave breaks (and if they are substantial enough, then a SSW can occur). The change in the stratospheric flow pattern can then start to feedback into the troposphere - changing the zonal flow pattern into something with more undulations and perhaps ultimately to a very meridional flow pattern especially if a SSW occurs - but not always. If the wave breaking occurs in one place then we see a wave 1 type displacement of the stratospheric vortex, and if the wave breaking occurs in two places at once then we will see a wave 2 type disturbance of the vortex which could ultimately squeeze the vortex on half and split it – and if these are strong enough then we would see a displacement SSW and split SSW respectively. The SSW is defined by a reversal of mean zonal mean winds from westerly to easterly at 60ºN and 10hPa. This definition is under review as there have been suggestions that other warmings of the stratosphere that cause severe disruption to the vortex could and should be included. http://birner.atmos.colostate.edu/papers/Butleretal_BAMS2014_submit.pdf A demonstration of the late January 2009 SSW that was witnessed in the first strat thread has been brilliantly formulated by Andrej (recretos) and can be seen below: The effects of a SSW can be transmitted into the troposphere as the downward propagation of the SSW occurs and this can have a number of consequences. There is a higher incidence of northern blocking after SSW’s but we are all aware that not every SSW leads to northern blocking. Any northern blocking can lead to cold air from the tropospheric Arctic flooding south and colder conditions to latitudes further south can ensue. There is often thought to be a time lag between a SSW and northern blocking from any downward propagation of negative mean zonal winds from the stratosphere. This has been quoted as up to 6 weeks though it can be a lot quicker if the polar vortex is ripped in two following a split SSW. A recent paper has shown how the modelling of SSW and strong vortex conditions have been modelled over a 4 week period. This has shown that there is an increase in accuracy following weak or strong vortex events – though the one area that the ECM overestimates blocking events following an SSW at week 4 is over Northwestern Eurasia. http://iopscience.iop.org/article/10.1088/1748-9326/10/10/104007 One noticeable aspect of the recent previous winters is how the stratosphere has been susceptible to wave breaking from the troposphere through the lower reaches of the polar stratosphere - not over the top as seen in the SSWs. This has led to periods of sustained tropospheric high latitude blocking and repeated lower disruption of the stratospheric polar vortex. This has coincided with a warmer stratosphere where the mean zonal winds have been reduced and has led to some of the most potent winter spells witnessed in recent years. We have also seen in recent years following Cohen's work the importance of the rate of Eurasian snow gain and coverage during October at latitudes below 60ºN. If this is above average then there is enhanced feedback from the troposphere into the stratosphere through the Rossby wave breaking pattern described above and diagrammatically below. Six stage Cohen Process: The effect of warming of the Arctic ocean leading to colder continents with anomalous wave activity penetrating the stratosphere has also been postulated http://www.tos.org/oceanography/archive/26-4_cohen.pdf As ever, I will supply links to various stratospheric websites were forecasts and data can be retrieved and hope for another fascinating year of monitoring the stratosphere. GFS: http://www.cpc.ncep.noaa.gov/products/stratosphere/strat_a_f/ ECM/Berlin Site: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html Netweather: https://www.netweather.tv/charts-and-data/stratosphere Instant weather maps: http://www.instantweathermaps.com/GFS-php/strat.php NASA Merra site: http://acdb-ext.gsfc.nasa.gov/Data_services/met/ann_data.html Previous stratosphere monitoring threads: 2016/17 https://www.netweather.tv/forum/topic/86485-stratosphere-temperature-watch-201617/ 2015/16 https://www.netweather.tv/forum/topic/84231-stratosphere-temperature-watch-20152016/ 2014/2015 https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/ 2013/2014 https://forum.netweather.tv/topic/78161-stratosphere-temperature-watch-20132014/ 2012/2013 https://forum.netweather.tv/topic/74587-stratosphere-temperature-watch-20122013/ 2011/2012 https://forum.netweather.tv/topic/71340-stratosphere-temperature-watch-20112012/ 2010/2012 https://forum.netweather.tv/topic/64621-stratosphere-temperature-watch/?hl=%20stratosphere%20%20temperature%20%20watch 2009/2010 https://forum.netweather.tv/topic/57364-stratosphere-temperature-watch/ 2008/2009 https://forum.netweather.tv/topic/50299-stratosphere-temperature-watch/
  3. A fresh new model thread as we start a cold spell. We've made a change this morning, and that is to start a new model tweet thread. The reason for this change is that a tweets are, by their nature brief, which in turn can leave them open to multiple interpretations, which in the fast-moving model thread can mean a lot of reaction to misinterpretations which pulls the whole thing off on a tangent. So please don't post tweets into this thread - keep them to the new thread. We've also started another new thread this week, and that's the In depth (chilled out) model thread, for those who want a slower paced look at the models. Cross-posting to this and the new thread is fine, the best route to doing this is to use the multiquote button (the + sign bottom left of the post), then when you go to post your new post, you'll see a button bottom right allowing you to quote the post & copy it over. If you're unsure where to find the models, head over to the Netweather Charts and Data homepage, where you'll have access to all the main ones - including our in house NetWx models, the SR hires version is particularly handy when it comes to forecasting snow showers at shorter range. As ever, please keep this thread to model discussion only - and that does mean actually discussing the output, not just moaning about it. If you want to moan, ramp, or even moan about ramps, please head over to the model banter thread:
  4. A new thread, for posting and discussing tweets about the forecast models currently. Please only post tweets in this thread, not the main model or banter threads. The reason for this change is that a tweets are, by their nature brief, which in turn can leave them open to multiple interpretations, which in the fast-moving model thread can mean a lot of reaction to misinterpretations which pulls the whole thing off on a tangent.
  5. To cater for those who prefer a slower pace, more in depth discussion around the models, we've decided to setup this new thread. So if the drama and excitement of the main model thread isn't quite your thing, then please feel free to post into this thread. You're also welcome to cross-post - so if you've made a longer post in the model thread, you can copy it into here, and vice-versa.
  6. Here we go then with the strat thread for autumn and winter 2016/17. Ed and Tony are both very busy with work and life at the moment, so I'm starting the thread rolling, and have copied Ed's (Chionomaniac's) superb opening post to last years thread below. Ed and Tony are both hoping to be about more as we move into the Winter. As we speak things are starting to look potentially quite interesting stratosphere wise, so there ought to be plenty to chat about! ------------------------------ Ed's opener from 2015/16 As ever, the first post will become both a reference thread and basic learning thread for those wanting to understand how the stratosphere may affect the winter tropospheric pattern, so forgive me for some repeat from previous years, but it is important that those new to the stratosphere have a place that they can be directed to in order to achieve a basic grasp of the subject. The stratosphere is the layer of the atmosphere situated between 10km and 50km above the earth. It is situated directly above the troposphere, the first layer of the atmosphere and the layer that is directly responsible for the weather that we receive at the surface. The boundary between the stratosphere and the troposphere is known as the tropopause. The air pressure ranges from around 100hPa at the lower levels of the stratosphere to below 1hPa at the upper levels. The middle stratosphere is often considered to be around the 10-30hPa level. Every winter the stratosphere cools down dramatically as less solar UV radiation is absorbed by the ozone content in the stratosphere. The increasing difference in the temperature between the North Pole and the latitudes further south creates a strong vortex – the wintertime stratospheric polar vortex. The colder the polar stratosphere in relation to that at mid latitudes, the stronger this vortex becomes. The stratospheric vortex has a strong relationship with the tropospheric vortex below. A strong stratospheric vortex will lead to a strong tropospheric vortex. This relationship is interdependent; conditions in the stratosphere will influence the troposphere whilst tropospheric atmospheric and wave conditions will influence the stratospheric state. At the surface the strength and position of the tropospheric vortex influences the type of weather that we are likely to experience. A strong polar vortex is more likely to herald a positive AO with the resultant jet stream track bringing warmer and wet southwesterly winds. A weaker polar vortex can contribute to a negative AO with the resultant mild wet weather tracking further south and a more blocked pattern the result. A negative AO will lead to a greater chance of colder air spreading to latitudes further south such as the UK. AO chart The stratosphere is a far more stable environment then the troposphere below it. However, the state of the stratosphere can be influenced by numerous factors – the current solar state, the Quasi Biennial Oscillation (QBO), the ozone content and distribution and transport mechanism, the snow cover and extent indices and the ENSO state to name the most significant. These factors can influence whether large tropospheric waves that can be deflected into the stratosphere can disrupt the stratospheric polar vortex to such an extent that it feeds back into the troposphere. Ozone Content in the stratosphere Ozone is important because it absorbs UV radiation in a process that warms the stratosphere. The Ozone is formed in the tropical stratosphere and transported to the polar stratosphere by a system known as the Brewer-Dobson-Circulation (the BDC). The strength of this circulation varies from year to year and can in turn be dictated by other influences. The ozone content in the polar stratosphere has been shown to be destroyed by CFC's permeating to the stratosphere from the troposphere. The overall ozone content in the polar stratosphere will help determine the underlying polar stratospheric temperature, with higher contents of ozone leading to a warmer polar stratosphere. The ozone levels can be monitored here: http://www.cpc.ncep.noaa.gov/products/stratosphere/sbuv2to/index.shtml One of the main influences on the stratospheric state is the QBO. This is a tropical stratospheric wind that descends in an easterly then westerly direction over a period of around 28 months. This can have a direct influence on the strength of the polar vortex in itself. The easterly (negative) phase is thought to contribute to a weakening of the stratospheric polar vortex, whilst a westerly (positive) phase is thought to increase the strength of the stratospheric vortex. However, in reality the exact timing and positioning of the QBO is not precise and the timing of the descending wave can be critical throughout the winter. Diagram of the descending phases of the QBO: (with thanks from http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo/index.html ) The QBO has been shown to influence the strength of the BDC, depending upon what phase it is in. The tropical upward momentum of ozone is stronger in the eQBO , whereas in the wQBO ozone transport is stronger into the lower mid latitudes, so less ozone will enter the upper tropical stratosphere to be transported to the polar stratosphere as can be seen in the following diagram. http://www.atmos-chem-phys.net/13/4563/2013/acp-13-4563-2013.pdf However, the direction of the QBO when combined with the level of solar flux has also been shown to influence the BDC. When the QBO is in a west phase during solar maximum there are more warming events in the stratosphere, as there is also during an easterly phase QBO during solar minimum, so the strength of the BDC is also affected by this – also known as the Holton Tan effect . http://strat-www.met.fu-berlin.de/labitzke/moreqbo/MZ-Labitzke-et-al-2006.pdf http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50424/abstract http://onlinelibrary.wiley.com/doi/10.1002/2013JD021352/abstract The QBO is measured at 30 hPa and has entered a westerly phase for this winter. As mentioned warming events are more likely during solar maximum when in this westerly phase – with the solar flux below 110 units. Currently, we have just experienced a weak solar maximum and the solar flux heading into winter is still around this mark. This doesn’t rule out warming events, but they will not be as likely – perhaps if the solar flux surges then the chance will increase. Latest solar flux F10.7cm: http://www.swpc.noaa.gov/products/solar-cycle-progression Sudden Stratospheric Warmings: One warming event that can occur in the stratospheric winter is a Sudden Stratospheric Warming (SSW) or also known as a Major Midwinter Warming (MMW). This, as the name suggests is a rather dramatic event. Normally the polar night jet at the boundary of the polar vortex demarcates the boundary between warmer mid latitude and colder polar stratospheric air (and ozone levels) and this is very difficult to penetrate. SSWs can be caused by large-scale planetary tropospheric (Rossby) waves being deflected up into the stratosphere and towards the North Pole, often after a strong mountain torque event. These waves can introduce warmer temperatures into the polar stratosphere which can seriously disrupt the stratospheric vortex, leading to a slowing or even reversal of the vortex. Any SSW will be triggered by the preceding tropospheric pattern - in fact the preceding troposheric pattern is important in disturbing the stratospheric vortex even without creating a SSW. Consider a tropospheric pattern where the flow is very zonal - rather like the positive AO phase in the diagram above. There has to be a mechanism to achieve a more negative AO or meridional pattern from this scenario and there is but it is not straightforward. It just doesn't occur without some type of driving mechanism. Yes, we need to look at the stratosphere - but if the stratosphere is already cold and a strong polar vortex established, then we need to look back into the troposphere. In some years the stratosphere will be more receptive to tropospheric interactions than others but we will still need a kickstart from the troposphere to feedback into the stratosphere. This kickstart will often come from the tropics in the form of pulses and patterns of convection. These can help determine the position and amplitude of the long wave undulations – Rossby waves - that are formed at the barrier between the tropospheric polar and Ferrel cells. The exact positioning of the Rossby waves will be influenced by (amongst other things) the pulses of tropical convection – such as the phase of the Madden Jullian Oscillation and the background ENSO state and that is why we monitor that so closely. These waves will interact with land masses and mountain ranges which can absorb or deflect the Rossby waves disrupting the wave pattern further - and this interaction and feedback between the tropical and polar systems is the basis of how the Global Wind Oscillation influences the global patterns. If the deflection of the Rossby Wave then a wave breaking event occurs – similar to a wave breaking on a beach – except this time the break is of atmospheric air masses. Rossby wave breaks that are directed poleward can have a greater influence on the stratosphere. The Rossby wave breaks in the troposphere can be demonstrated by this diagram below – RWB diagram: https://www.jstage.jst.go.jp/article/jmsj/86/5/86_5_613/_pdf This occurs a number of times during a typical winter and is more pronounced in the Northern Hemisphere due to the greater land mass area. Most wave deflections into the stratosphere do change the stratospheric vortex flow pattern - this will be greater if the stratosphere is more receptive to these wave breaks (and if they are substantial enough, then a SSW can occur). The change in the stratospheric flow pattern can then start to feedback into the troposphere - changing the zonal flow pattern into something with more undulations and perhaps ultimately to a very meridional flow pattern especially if a SSW occurs - but not always. If the wave breaking occurs in one place then we see a wave 1 type displacement of the stratospheric vortex, and if the wave breaking occurs in two places at once then we will see a wave 2 type disturbance of the vortex which could ultimately squeeze the vortex on half and split it – and if these are strong enough then we would see a displacement SSW and split SSW respectively. The SSW is defined by a reversal of mean zonal mean winds from westerly to easterly at 60ºN and 10hPa. This definition is under review as there have been suggestions that other warmings of the stratosphere that cause severe disruption to the vortex could and should be included. http://birner.atmos.colostate.edu/papers/Butleretal_BAMS2014_submit.pdf A demonstration of the late January 2009 SSW that was witnessed in the first strat thread has been brilliantly formulated by Andrej (recretos) and can be seen below: The effects of a SSW can be transmitted into the troposphere as the downward propagation of the SSW occurs and this can have a number of consequences. There is a higher incidence of northern blocking after SSW’s but we are all aware that not every SSW leads to northern blocking. Any northern blocking can lead to cold air from the tropospheric Arctic flooding south and colder conditions to latitudes further south can ensue. There is often thought to be a time lag between a SSW and northern blocking from any downward propagation of negative mean zonal winds from the stratosphere. This has been quoted as up to 6 weeks though it can be a lot quicker if the polar vortex is ripped in two following a split SSW. A recent paper has shown how the modelling of SSW and strong vortex conditions have been modelled over a 4 week period. This has shown that there is an increase in accuracy following weak or strong vortex events – though the one area that the ECM overestimates blocking events following an SSW at week 4 is over Northwestern Eurasia. http://iopscience.iop.org/article/10.1088/1748-9326/10/10/104007 One noticeable aspect of the recent previous winters is how the stratosphere has been susceptible to wave breaking from the troposphere through the lower reaches of the polar stratosphere - not over the top as seen in the SSWs. This has led to periods of sustained tropospheric high latitude blocking and repeated lower disruption of the stratospheric polar vortex. This has coincided with a warmer stratosphere where the mean zonal winds have been reduced and has led to some of the most potent winter spells witnessed in recent years. We have also seen in recent years following Cohen's work the importance of the rate of Eurasian snow gain and coverage during October at latitudes below 60ºN. If this is above average then there is enhanced feedback from the troposphere into the stratosphere through the Rossby wave breaking pattern described above and diagrammatically below. Six stage Cohen Process: The effect of warming of the Arctic ocean leading to colder continents with anomalous wave activity penetrating the stratosphere has also been postulated http://www.tos.org/oceanography/archive/26-4_cohen.pdf Last year we saw a large snow gain but unfortunately tropospheric atmospheric patterns prevented the full potential of these being unleashed on the stratosphere – hence no SSW, but this winter could be different, but we will have to wait until the end of October. ENSO Influences One of the main influences in the global atmospheric state this winter will be the upcoming El Nino, and that is forecast to be the strongest since 1997. Studies have shown that SSW’s are more likely during strong ENSO events ( http://www.columbia.edu/~lmp/paps/butler+polvani-GRL-2011.pdf) but also that there is a particular pattern of upward propagating waves. During El Nino events wave formation is suppressed over the Indian Ocean Basin whilst it is enhanced over the Pacific Ocean http://link.springer.com/article/10.1007%2Fs00382-015-2797-5 The ENSO pathway taken may be all critical this year as can be demonstrated by this paper http://www.columbia.edu/~lmp/paps/butler+polvani+deser-ERL-2014.pdf This can lead us to suggest that a rather distinctive wave 1 pattern is likely this winter with the trigger zone likely to be over the north Pacific in the form of a quasi stationary enhanced wave 1 – a traditional Aleutian low SSW trigger pattern is suggested by Garfinkel et al ( http://www.columbia.edu/~lmp/paps/garfinkel+etal-JGR-2012.pdf ) and this should be expected at some point this winter. The reported incidence of SSW in EL Nino years is roughly around 60% - which is more than ENSO neutral years. A big question remains however, whether the ENSO wave 1 pattern will override the negative HT effect that the wQBO with the reducing solar ouput link brings. And even if it does, and we do achieve a displacement SSW, the next question is how will this affect the Atlantic sector of the Northern Hemisphere? My suspicion is that even if we do achieve a SSW this winter it will be in the second half, and also any subsequent blocking may not be quite right for the UK and, that if we were to achieve a –ve NAO, any block will be nearer Canada than Iceland, leaving the Atlantic door ajar. It is still too early this winter to be making any definitive forecasts – the next 6 weeks are very important stratospherically, determining in what vein winter will start. Already we are seeing a forecast of weak wave activity disrupting the growing vortex and it will be interesting to see if this is repeated during November. And it will be especially interesting to see what occurs in November and what is forecast for December before winter starts because typical strong El nino wQBO stratospheric composite analogues tell an opposite story. They suggest that the stratospheric vortex will be disrupted and weaker early in the winter before gaining in strength by February. December: January February The mean zonal winds are already forecast to be below average so perhaps an early disrupted vortex is more likely this year! As ever, I will supply links to various stratospheric websites were forecasts and data can be retrieved and hope for another fascinating year of monitoring the stratosphere. GFS: http://www.cpc.ncep.noaa.gov/products/stratosphere/strat_a_f/ ECM/Berlin Site: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html Netweather: http://www.netweather.tv/index.cgi?action=stratosphere;sess=75784a98eafe97c5977e66aa65ae7d28 Instant weather maps: http://www.instantweathermaps.com/GFS-php/strat.php NASA Merra site: http://acdb-ext.gsfc.nasa.gov/Data_services/met/ann_data.html Previous stratosphere monitoring threads: 2015/16 https://www.netweather.tv/forum/topic/84231-stratosphere-temperature-watch-20152016/ 2014/2015 https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/ 2013/2014 https://forum.netweather.tv/topic/78161-stratosphere-temperature-watch-20132014/ 2012/2013 https://forum.netweather.tv/topic/74587-stratosphere-temperature-watch-20122013/ 2011/2012 https://forum.netweather.tv/topic/71340-stratosphere-temperature-watch-20112012/ 2010/2012 https://forum.netweather.tv/topic/64621-stratosphere-temperature-watch/?hl=%20stratosphere%20%20temperature%20%20watch 2009/2010 https://forum.netweather.tv/topic/57364-stratosphere-temperature-watch/ 2008/2009 https://forum.netweather.tv/topic/50299-stratosphere-temperature-watch/
  7. CFS anomalies

    Having viewed the latest longer-range Youtube video from Weatherweb (video embedded below), in which the CFS anomaly output was apparently swaying that company's thoughts regarding February's weather towards a flatter, zonal pattern), I posted the link (complete with an attempt at model-related discussion) in the relevant Model Output thread. More than one poster remarked that, in their opinion, this model was generally inaccurate and not to be trusted. I know that several senior posters use anomalies as a means of smoothing-out inter-run variations, so I was wondering if the CFS anomaly output is produced in a similar manner to others, and why it appears to be perceived as less useful? Thanks.
  8. Seen a lot of discussion about a torpedo in the model thread and frankly don't understand: What is it? What weather wild it bring? When is it? How can we be so sure this far out?
  9. The Model Dictionary

    Have you ever read the Model Output Discussion/Techical Model thread and wondered what some of the terms mean? This thread will provide you with the low-down on various model terms, as well as brief explanations about the variety of models that exist. 'The Model Dictionary' is ideal for beginners and those of you who want to improve your model output knowledge even further (but do read some of the posts in the Model Output and Model Technical threads, too, as you can learn a lot from the knowledgeable posters in those threads). The Model Dictionary may also be useful for those of you wanting to start constructing your own model output posts. However, the Learner's Area of the Netweather Forum is recommended for checking out additional information, model reading tips and for much more detailed versions of any of the terms covered here. http://forum.netweather.tv/forum/24-learning-about-weather-and-meteorology/ (and) http://forum.netweather.tv/forum/5-the-netweather-guides/. If anyone has any model terms that they want added to the dictionary, or any existing terms that could do with being modified/improved, feel free to post your suggestions here and I'll update the thread with the new and modified terms. (If it comes to the point that the option to edit this post is no longer possible, I'll post the updated versions of this glossary as occasional new posts). A Amplification - When amplification occurs within the weather pattern. It is a bumpy looking pattern on the models' pressure charts where the general airflow becomes all wavy, usually thanks to pronounced ridges of High Pressure systems and notable *troughing of Low Pressure systems between the ridging High Pressure cells (*see 'Troughs' for more information). For example, you might get a long flat Westerly airflow over the UK that becomes more and more wavier as the pattern tries to amplify and High Pressure in the Atlantic tries to send some of its ridging Northwards to the West of us. Fairly potent periods of cool/cold North-Westerly winds can occur that spill down along the High Pressure system's Eastern side towards the UK. The amplification of the Jet Stream also helps along with a pressure pattern becoming all 'bumpy'. You can also get some portions of the pattern that's amplified and some portions that are flatter. Amplified patterns can, but not always, lead to Atlantic and/or Northern blocking further down a line, such as a High Pressure system trying to ridge in above us from the South. An example of an amplified pattern: The black arrows shows the bumpiness of the pattern and the general airflow(s). Atlantic Blocking - A High Pressure system that sets itself up either over us, to the West of us, or to East of us and stops the normal travel of the West to East progression of Atlantic Low Pressure systems/depressions. Effectively, the High Pressure system acts as a 'block' deflecting the Lows away from the UK. Azores High - An area of High Pressure that hangs about to our South West in the Atlantic Ocean. It contributes to some of the weather in the UK where it sometimes extends some of its ridging towards us bringing warm or hot spells during the Summer. B Bartlett High - Cold and snow fans worst nightmare during the Winter. Mwha ha ha ha haa! It is an area of heights that sit stubbornly to our South-East. The High Pressure system can be very hard to budge. You can go weeks and weeks with winds coming from a mild South-Westerly direction with approaching Low Pressure systems from our West forced to track North-Eastwards. Spells of rain can occur fairly frequently as well, most especially to the North-West where the Low Pressure is more influential. Occasional wintry outbreaks of sleet and snow can happen (mostly for high-ground, but not necessarily so) via brief occurrences of winds swinging to a cool/cold Westerly or North-Westerly direction. The Bartlett High was named after the weather forecaster, Paul Bartlett. The below chart shows a Bartlett High to our South and South-East, with a long draw of winds from the South-West. The Southern part of the UK would see the most mildest conditions in this setup, while much further North, it would be cooler: BI - Stands for British Isles. The shortened form of this is sometimes used in the model output thread. Blocking - Where High Pressure systems set themselves up in places that interrupts the normal flow of weather patterns. Essentially, the High Pressure systems behave like a 'block'. (see 'Atlantic blocking' and 'Northern blocking' for examples). C Channel Low - Pretty much what the words refer to - A Low Pressure system over the Channel. In Winter, a channel Low often often brings spells of sleet and snow on its Northern side over the Southern UK as it engages with cold air to the East/North-East. A number of times, though, the very far South of the UK will just experience rain instead with milder air from the South being more influential. Black circle showing a Channel Low. CFS - Stands for 'Coupled Forecasting System'. It belongs to the same organization that produces the GFS model - NCEP. Generating charts up to 9 months ahead (yep, you heard that right), it is a long range model. But to use it effectively, the model should only really be used for trend spotting. It also produces anomaly charts up to several months ahead and this can also be useful for trend spotting. For example, if the anomaly charts have been continually producing a cold, blocked outlook for Christmas with higher than average heights to the North and lower than average heights to the South, then it could very well be the route we would head in. While charts for several months ahead will understandably change a huge amount, the CFS has been known to be close to perfect with some of its outlooks that have trended in the past. However, if you were ever interested in long range weather forecasting, this site: http://www.weatherweb.net/wxwebchartscfshowtouse.php provides some useful tips on how to use charts like this effectively... 1. Take a long view - step back from the charts and see how the weather is affecting large geographical areas, such as the whole of Europe. 2. Spot extremes - Look for any extremes of weather, heavy rain, high temperatures. 3. Visit daily - Take a look at the forecasts each day. This helps builds a picture of consistency; the more consistent the model from day to day, the more confidence you can have in it. 4. Don't take it literally - The CFS can only give guidance, not a forecast! Just because it says a particular day in 3 weeks may be warm, that doesn't mean that it will be, it should be taken that there is a chance of warmer weather during that period. 5. Look at each of the members and look for consistency between each. One should exercise caution when using long range forecasting models such as the GFS. They should be used for guidance only, but the experience of using these is that they are better than nothing at all! D E ECMWF - Stands for 'European Centre for Medium-Range Weather Forecasts'. A European weather model. Some people use the term 'ECM' as its shortened version. It is regarded as one of the best performing models out their. As a general rule, the ECMWF is supposed to be better than the GFS at handling blocking patterns to the East, while the GFS is supposed to be better than the ECMWF (though not always) at handling developments to the North-West of us. And sometimes this can have a huge impact as to what happens over the UK. It is one reason why the GFS tends to pick out Northerly setups (with cool/cold air flowing down from the North) earlier than the European model. This model updates twice a day and goes up to 240 hours (10 days) ahead. Made up of the 00Z and the 12Z runs. Ensembles - What happens here is that an operational model run (main model run) is re-produced again at a lower resolution. This is then referred to as the 'control run'. Variations of this run are produced, each of which with different starting conditions. Along with the main operational model run, the results are then recorded as a line graph - each of these lines can be referred to as 'ensemble members'. They show various possibilities that could occur in regards to the weather. This is supposed to increase accuracy and help determine whether the particular operational model run is worth taking seriously or not. Most times you will find that the ensembles tell the bigger story of what will happen, than what the main model run shows. You can view various ensemble graphs, such as... [*]Air-Pressure [*]850 hPa Upper Temperatures [*]Precipitation amounts [*]Average Temperatures You can also select what the ensembles show for your nearby region or town. How ever close the lines are on the graph reflects the confidence the model and its ensemble members has on a particular weather outlook. Underneath is an example of the Sea Level Pressure for London using GFS's ensembles: (GFS's ensemble set is also known as the 'GEFS ensembles') The X axis shows the days ahead, while the Y axis shows the numbers relating to the type of weather, climate or atmospheric condition it is. The further along the graph you go, the more the ensemble members' confidence reduces, and thus the lines on the graph begin to scatter. The period at where the lines start to scatter depends on how well the operational model and its ensemble members are handling particular weather patterns. As you would likely expect, you can see that the lines for the first few days ahead are close together and reflects the confidence the GFS and its members has on the atmospheric conditions. The ensembles generally agree to a slight pressure drop around the 4th October (the dip between the 3rd October and the 5th October), with the pressure rising after that. Except for the odd ensemble member, the period at where the lines start to scatter becomes noticeable past the 7th October, with various solutions on offer. The red line (the ensemble mean) is the mean average of all of the ensemble members' outcomes. You can view the model's ensemble mean as an actual graphical model chart and see how it compares to the operational graphical model chart. An example using the ECMWF's 00Z '500 hPa and Sea Level Pressure' ensemble mean chart (with the operational ECMWF 00Z '500 hPa and Sea Level Pressure' chart below it). Both of these showing the pressure conditions at 240 hours ahead: Since the ensemble mean is just an mean average of what the ensemble members show, and since the operational model run and its ensemble members' confidence drop the further ahead they predict, this will explain why the ensemble mean chart becomes less detailed the further ahead you're viewing it. It sort of works out a middle-ground-like solution of what its ensemble members show regarding what the weather conditions might be like several days ahead. The first few time-frames of the ensemble mean tends to be as detailed as the actual operational model run, and both will follow each other very closely, because of their high confidence in regards to the weather for the next few days. On the above example, however, the 00Z ECMWF ensemble mean expects that the High Pressure to the North-East of the UK on the operational model run will be more concentrated towards the East of the UK. Nor does the ensemble mean show the High Pressure to the East linking up with High Pressure over Greenland, like it does on the operational model run. This could mean that the operational ECMWF run has probably over-estimated the Northwards placement of the High Pressure to the North-East, and that it should be slightly further South/South-Eastwards. And if this was the case, then the operational run has probably also over-estimated how easily its High Pressure system to the North-East links up with the Greenland High Pressure system. For tend-spotting purposes, keeping an eye on future ensemble means and their ensembles from some of the models, can be handy to see where they keep heading in. Comparing a different operational model to an ensemble mean chart is probably a good idea as well, to see how close their outlook relates to each other. Should the operational outlook from a different model follow the ensemble mean closely all the way through, that could provide extra reassurance that the ensemble mean is heading in the right direction. It can actually sometimes be much more reliable to follow the ensemble mean, rather than the operational model run, especially since the operational run only represents one line on an ensemble graph (the green one on the GFS's ensemble graph, for example), and can easily become an big 'outlier' in parts in relation to the ensemble mean, or even in relation to the other lines on the graph. In fact, you can see that the GFS operational run shows the biggest pressure drop around the 15th October on its ensemble graph, and doesn't follow the ensemble mean closely at all around that period, so its chances of coming off are almost virtually zero (unless I suppose another operational model run just happens to show very Low Pressure over the London area for 15th October, in which case its chances of coming off might be a little higher). This is why, however, if you're viewing the main model run, its worth checking the ensembles to see how well they follow the operational model run. If there is not much support for that run at all, then it's a good reason to be particularly cautious of what the operational model shows for a fair amount of days ahead. It's true that since a model's outlook several days ahead is liable to change a lot from one run to another that we shouldn't really trust what any run shows beyond a particular period. But it's still worth checking the main model run against the ensembles to see how confident the operational model run really could be and to see if any trends can be spotted. If the ensemble mean, let's say, continues to show a slight downward trend in pressure, with the general scatter of the other lines on the graph shaping out a slight downward trend, it could be a good sign to where we could head in the future in regards to the air-pressure. For the sake of it, though, it is a good idea to also see what other main models runs are producing in relation to the one you're viewing, because even if a GFS operational model run may have strong ensemble support, it may not always mean too much if the other main operational models (such as the ECMWF, UKMO) completely disagree with GFS's weather scenarios. Either, it could mean the GFS and its ensembles are heading the wrong way, or that the other models are just not picking out the solutions the GFS and its ensembles show. What I will say, though, is even if their is notable large differences between the various models, which ever one has the strongest ensemble support is the one that is likely to lead the way in regards to its outlook. This could be particularly true if the GFS, on its last few runs, has continued to stick to a particular solution with its ensembles continuing to support it (John Holmes, though, does recommend comparing only the 00Z and 12Z GFS runs with each other, rather than all four of the GFS's daily runs when looking for trends). Also, if the other models have continued to offer solutions that vary widely from one run to another, then it's a good chance that they are not quite getting to grips with the weather outlook for the future. This doesn't always last, though, as models (and even the ensembles, especially if they're trending in the wrong way) do go through phrases where they won't perform as well as they could do. F Fantasy Island - 'FI' for short. A term used to refer to a time-frame in the models where the accuracy in their predictions severely reduces. Usually around the 168 hour period and beyond in the models' outlooks - the sort of period where their outlooks become fantasy and dreamland-like, hence the term 'Fantasy Island'. However, if the models are having a tough time handling a particular pattern, people may use the 'FI' term for a time-frame in the models earlier than 168 hours. If, let's say, their are some fairly huge differences between the GFS, ECMWF and UKMO models as early as 96 hours, then this could count as Fantasy Island due to the uncertainty of the models' outcomes within that period. It should also be noted that some people use phrases such as "this model disagrees with another model" to refer to the differences in the evolutions the models show. Although a chart's FI outlook is unlikely to come off, occasionally it can happen. This is especially true if a model has picked up a trend regarding a particular pattern in its last few updates, and also if it has ensemble support. FAX Charts - White in colour, they are hand drawn by the Met Office, and are similar to the Pressure charts shown on the main models such as the GFS, ECMWF, UKMO and so on, but only without all the pretty colours in the background (although this is only true if you're viewing the '500 hPa Sea Level Pressure' charts from the GFS, UKMO etc, which have the rainbowy colours in it, rather than the just the 'Sea Level Pressure' charts - see example below). ('500 hPa and Sea Level Pressure' chart - has the colours of the rainbow in it) ('Sea Level Pressure' chart without the 500 hPa's - doesn't have the colours of the rainbow in it) One advantage of FAX charts, over other kinds of charts, is because of the human input involved with this chart, they can be rather accurate - even up to 120 hours ahead. When the Met Office generate these charts, they look at the data from various models from the likes of their own UKMO models, the ECMWF, the JMA, the GFS and other data from the Met Office's super-computers. Due to some accuracy issues of the GFS model, the Met Office may not always include this model when basing their conclusions from the outlooks shown on various charts. As such, you will likely find that Met Office's FAX charts are very reminiscent of the pressure charts from the UKMO and/or ECMWF models. FAX charts contain various symbols and features on them: [*]Low Pressure systems are marked by an 'L', while High Pressure systems are marked by an 'H'. [*]The bold black line with the semi-circles on it represents a 'warm front'. [*]The bold black line with the pointy triangles on it represents a 'cold front'. [*]The bold black line with both the semi-circles and the triangles on it is an 'occluded front'. [*]The bold black line with no triangles or semi-circles on it represents an 'upper trough' Which ever way the semi-circles and triangles are pointing in shows the direction of travel of the weather fronts. The FAX charts are viewable up to 120 hours ahead. G GFS - Stands for 'Global Forecasting System'. An American Weather Model. Created by NCEP. It contains billions of different types of charts, such as the standard pressure charts, convection potential, precipitation and its types, temperature charts and many more. This model, however, does come with a few issues: Whilst no model is entirely perfect, the GFS has the tendency to be over eager with the progression Low Pressure systems make from West to East, hence the term "the GFS is being too progressive" may be used in the model output thread. It can also have the habit of over-deepening Low Pressure systems (although it is not necessarily the only model that does this). NCEP often make adjustments to the model to further improve its performance. This model updates four times a day and goes up to 384 hours (16 days) ahead. It is made up of the runs: 00Z, 06Z, 12Z and 18Z. GEM - Stands for 'Global Enviromental Multiscale' model. It can be a suitable model for medium range forecasting and it has fairly good performance overall. The ECMWF and GFS are its only real competitors in that they are the only two other models that go up to ten days ahead and beyond (bar the ECM 32 day model and CFS long range model). The GEM updates twice a day and is made up of the following runs: 00Z and 12Z. H High Pressure - 'HP' for short. Areas of stronger than average pressure - usually around 1016 hPa/millibars or higher - that fill up the gaps in the atmosphere between and around Low Pressure systems. Broadly speaking, they are not quite as circular as Low Pressure systems (though not all Lows are round). They tend to be oval or sausage-shaped and will often bring settled, calm conditions. How sunny it will be depends on the orientation and positioning of a High Pressure system. As an example for the UK, if you want warm, sunny weather, ideally the High Pressure needs to hang about just to our East with Southerly/South-Easterly winds drawing up warm, dry air from the continent. Wind tends not to be an issue with High Pressure systems - the isobars are usually well spaced out. In fact, if you're stuck under the centre of a High Pressure system, their may not be any wind at all. Winds, will, however, circulate clockwise around High Pressure cells. 'Anticyclone' is an alternative word people use to refer to areas of High Pressure. Black circle showing an area of High Pressure I J Jet Stream - Fairly narrow passages of fast high-level winds - about 30,000 meters above the Earth's surface. You could almost think of it as various pathways that direct Low Pressure systems along it, and can be one of the main controllers of our weather. Depending on the positioning of Jet Stream and where passages of high-levels winds flow along, it can have an affect on where High Pressure systems migrate to, and how pronounced their ridging is. You often get one of the main streams of the Jet flowing Eastwards through from America, all the way through to the UK, or just to the North of it. In Summer, the normal position of the main stream of the Jet is to the North of us, although in some of the recent Summers, with the exception of Summer 2013, it has been behaving very strangely - the main stream of the Jet going much further South than usual steering constant Lows over, or to the South of us. Where you find both the cold air to the North and the hot air to the South meet is where the main stream of the Jet tends to flow along (or at least close to this boundary). When ever heights build to our North, this can force the main area of the Jet Stream to go South, although there has also been debates about whether the arctic sea-ice melt has affected the normal flow and positioning of the Jet Stream. When the Jet Stream becomes weak, or fragmented, with streams of the Jet split into pieces, Atlantic or Northern blocking may occur, just like what a very amplified pattern could cause. Some Jet Stream examples underneath: Example 1: In this situation, you have one of the main areas of the Jet Stream flowing to the South of us attempting to bring a Low Pressure system to the South-West of us. The cyclone collides against the High Pressure to the North-East of us thanks to the slight West-South-West alignment of the Jet stream to the South-West of us. And this is kind of helping to steer the Low Pressure up against the High to our North-East. The Low does not quite slide underneath the High, despite one of the main areas of the Jet Stream being to the South/South-West of the UK. Example 2: In this example, you have an area of a stream of the Jet flowing on a South-West to North-East direction to the North-West of the UK. The stream of the Jet then curves back down Southwards through the North-Sea to the East of the UK. But the curvy Jet to the North of the UK is still far enough North to allow a High from the South or South-West to build some of its heights North-Eastwards over the UK. A South-West to North-East alignment of the Jet with it staying out to the North-West of the UK often allows High Pressure systems from the South or South-West to ridge North-Eastwards towards us. One other aspect about the Jet Stream is that it can sometimes split up into two main streams - one going to our South, and another going to our North. In this type of setup, the GFS apparently has a slight bias of overdoing the power of the main stream of the Jet going to the North of us. JMA - Stands for 'Japan Meteorological Agency'. One of the slightly less well-known models, although it runs a MSM (Meso-Scale Model - these are short range models) to provide small forecasts in Japan. The JMA model can be a useful asset to weather operations across the globe. It is highly regarded by the UKMO and can occasionally pick out certain weather patterns earlier than some of the other models. This model updates twice a day and goes up to 192 hours ahead. It is made up of the 00Z and 12Z runs. K L Low Pressure - 'LP' for short. Often circular or elongated in shape, they are areas of lower than average pressure - usually around 1012 hPa/millibars and below - that fill up the gaps between and around High Pressure systems in the atmosphere. They bring with them unsettled and changeable weather such as frontal bands of rain or snow, sunshine and showers... and even storms! The weather can be windy too, but the tighter the spaces between the isobars (white or black lines on the charts that mark out the Low and High Pressure cells) the windier the weather is likely to be, although the Jet Stream can have an impact on this as well. The winds spin anti-clockwise around Low Pressure systems. Low Pressure systems can also be referred to as 'Cyclones'. Another aspect about Low Pressure systems is that they come in different intensities: Deep Lows have a central pressure area lower than 980 hPa, while moderate Lows are those with a centre of around 980 to 1000 hPa. Shallow Lows are those that are around 1000 hPa, or higher. Furthermore, Lows can have a habit of 'filling out' if the centre of the cyclone becomes less and less deeper. Black circle showing an area of Low Pressure: M Model Posers - People, especially ladies, who pose as 'models' in magazines, newspapers, TV shows etc. Avoid talking about this type of model in the Model Output thread as it is off-topic and the Netweather moderators might banish you from the forum. Forever! (although if you're lucky, Chinomaniac and his moderating crew might give you a second chance). ;-) N NAVGEM - Stands for 'Navy Global Environmental Model'. There's quite an interesting tale behind this model. It never used to be the NAVGEM model. The former model, NOGAPS, used to run all the time. That model became discontinued and the NAVGEM replaced it. And it's very unlikely the NOGAPS model will be brought back to life. Knowing the NOGAPS was gone brought tears to the eyes of some of those who liked that model so much. But it's not all bad as the NAVGEM has supposedly had improvements done to it to increase its performance potential. Just like the expired NOGAPS, this model updates four times a day. It is made up of the following runs: 00Z, 06Z, 12Z and 18Z. NMM - A Meso-scale Model which runs at a very high resolution of 12 kilometers. According to Paul, "it is high enough resolution to pick out small more localised weather features that lower resolution models will miss." (http://forum.netweather.tv/blog/189/entry-3452-new-nmm-hi-res-forecast-model-for-the-uk/). This means it can pick out even more details than the GFS model and even the ECMWF model - both of which are run at lower resolutions. (You can find more about the models' resolutions here: http://forum.netweather.tv/topic/72326-model-resolution/ - credit goes to lorenzo). The NMM is a short range model and it updates twice a day, but you need a Netweather Extra subscription to view it. Northern Blocking - Cold and snow fans number one setup in Winter. It is where blocking occurs to the North of us, and/or over the Artic region via High Pressure building to the North of us. Ideally, over the UK, you do not want High Pressure system(s) to the North of us to be too far North, otherwise Lows out West may not track far enough South to deliver cold South-Easterly, Easterly, or North-Easterly winds on their Northern side. When the Northern blocking is significant, such as a strong Greenland High Pressure system linking up with a Scandinavian High Pressure system (and with it being very close by to the North of the UK), this forces the Jet Stream to send a fair amount of its energy to the South of us and we can become locked into a prolonged cold spell with winds constantly coming in from an Easterly direction. An example during late November 2010, where a High Pressure system to our North provided the UK with some chilly Easterly/North-Easterly winds: At times, shortwaves, troughs or small Lows, usually over the Norway (or Scandinavia) area, will try to separate the link up of a High Pressure system to the North-West of us and a High Pressure system to the North-East of us into two, like so: But in the case of the 1947 example above, it might get itself trapped inside the High Pressure systems... An aspect you have to be careful of is that the Northern blocking isn't very weak as Low Pressure systems from below and above could easily attack the High Pressure system(s) destroying the blocking to the North. And, as such, we could easily revert back to a milder pattern with Westerly or South-Westerly winds. And this would be especially true if the Jet Steam tries to power back through over us from the West without it no longer staying to the South of us. Northern blocking can also become eradicated, if one of the streams of the Jet powers back up to the North and sends most of its energy and associated Low Pressure systems over the top of the blocking High(s) to our North and forces the High Pressure system(s) to sink Southwards over us. Northerly Toppler - A short lasting period where cool or cold winds flow down from the North. High Pressure from the West is forced to 'spill' over us cutting off the Northerly flow, with Westerly or South-Westerly winds returning from the West. But sometimes, approaching Lows from the West might just flatten out an amplified High Pressure system to our West (but with the Northerly airflow still destroyed). Northerly topplers often last for around 2 days; perhaps longer, if a High Pressure system to our West is particularly strong and can withstand the power of the West to East track of the Lows for a few extra days. Despite this, one reason why Northerly airflows and Northerly topplers don't last too long is not only because they 'topple' or get broken down easily, but because of a strong stream of the Jet is always keen to try and blast through a block to the West of us. The Jet Stream is an enemy of the Northerly! Northerlies via a Greenland High, though, will tend to last longer and the chances of them toppling so easily is much less likely. The charts below show the process for one of the types of 'Northerly Topplers' that happen. Example used from the period ' 26th January to 29th January 1935': The Northerly Toppler part 1 - The Northerly airflow beings to get established with Low Pressure to our North-East, and an amplified High Pressure to our West. (dark blue arrows showing cold air draining down from the North) The Northerly Toppler part 2 - The whole of the UK gets affected by a direct Northerly, although warmer South-Westerly winds (indicated by the red arrows with Low Pressure to the North) try to blow over the top of the High Pressure, and it slowly begins to get knocked Eastwards/South-Eastwards towards us. (the black arrows show it slowly beginning to get knocked over towards our direction) The Northerly Toppler part 3 - The Northerly has almost toppled completely, with only the South-Eastern UK holding onto cold air, which is now coming from the North-East, rather than directly from the North. This is thanks to Low Pressure to the North-West of the UK knocking a portion of the High Pressure system over us, and the far North of the UK begins to get affected by milder Westerly or South-Westerly winds (shown by the red arrows). The Northerly Toppler part 4 - It's game over for the Northerly! And the cold North-Easterly airflow now becomes concentrated over France and also areas further South-East, East, and North-East of it. The Low Pressure system which knocked a portion of the High Pressure over us, slowly makes a getaway North-Eastwards, and the orientation of the airflow over the UK is now a less-cold slack North-Westerly airflow. O Outlier - Where either a model's operational run, control run, or a variation of its control run is out of place amongst the other runs on the ensemble graph. The line representing the 'outlier' on a ensemble graph is very spaced out in relation to other lines on the graph, and is a good indication that the ensemble member's outlook is very unlikely to materialize. On the London ensemble graph example, the black circle shows how one of the lines looks out of place amongst the other lines, although it does start meeting up with other lines towards the end of the graph. As such, an ensemble member won't be an outlier all the way through - especially at the beginning, where the ensemble members' confidence are high with the tight clustering of the lines. You can get the odd time, where one or two of the 'outliers' on a ensemble graph may have detected a new trend, and the other ensemble members (including the operational and control run), may follow suit on future runs. P Performance Statistics - Various checks are carried out on the models. And their performance in regards to how they've handled pressure patterns, and other atmospheric conditions, are recorded in numbers and graphs. You can view how accurate the models have been handling various atmospheric weather patterns here (although this is where it starts to get rather technical: http://www.emc.ncep.noaa.gov/gmb/STATS/STATS.html / http://www.emc.ncep.noaa.gov/gmb/STATS/html/new_acz6.html) As an example, the Performance Statistics graph posted above shows the anomaly corrections of how well the various models have handled the 500 hPa and air pressure patterns in the Northern hemisphere in the last 31 days. The numbers on the Y axis on the graph relates to how well the models have handled the pressure patterns six days ahead. '1' means that a model handled the pressure patterns entirely perfectly with no errors whatsoever, while '0.2' means that a model was way off in the handling of their pressure patterns. Currently, the ECMWF model - the one in red - is performing the strongest with it receiving the highest average score of 0.808. The UKMO model, however - the one in orange - is close behind with an average score of 0.787. You can also see that the red line on the graph (representing the ECMWF) has generally been a touch higher than all the other lines on the graph (representing the other models) in the last 31 days. But their have been a few occasional brief periods within the last 31 days where the UKMO (representing the orange line) has been higher than the ECMWF's line. One other aspect about this type of graph is if it has the 'NHX' part in its name, it's for the Northern hemisphere, and if it has the 'SHX' part in its name, it's for the Southern hemisphere. Polar Maritime - 'Pm' for short. An airflow that comes from a cool/cold region from the North-West, usually with a fairly amplified High Pressure system just to the West or South-West of us. It's a type of North-Westerly airflow that is fairly common over the UK and can usually bring a sunshine and shower setup if the air is unstable enough. Cool or cold 850 hPa upper temperatures usually help with the instability. In Winter, if the cold Upper Temperatures coming down from the North-West haven't been moderated enough by the warmish Atlantic seas, some of the showers can fall as snow, most especially in the North-West of the UK and over high ground. But in Summer, when daylight heating from the Sun plays a big role, the temperatures over the land become warmer than that of the ocean temperatures, and you will find that the heaviest showers become concentrated more towards the Eastern side of Britain. Underneath is an example of a Polar Maritime airmass with Low Pressure to the North bringing cold air down from the North-West through the UK. (dark blue arrows showing direction of the airflow's travel). Polar Vortex - Blobs of dark blues and purples shown on the '500hPa Thickness and Sea Level Pressure' charts from ECMWF, GFS, UKMO, JMA, GEM, GME, NAVGEM etc. Some people will refer to the Polar Vortex as the 'PV'. But it is essentially like an area of Low Pressure systems that, in our part of the world, dominate the Northern Hemisphere with High Pressure systems surrounding it. The Polar Vortex occupies the Stratosphere and upper Troposphere levels and contains lots of very cold air. During the Winter where it gets very strong, Low Pressure systems become more powerful and increase in size as the Polar Vortex adds 'fuel' to them. This is thanks to lots of very cold air getting mixed in with warm air further South resulting in some very powerful Lows. But as the affects of the Polar Vortex weakens significantly during Summer, Low Pressure systems tend to be much smaller in size and less powerful. The '500 hPa and Sea Level Pressure' chart below [which I nicked from an old Model Output Discussion thread ;-)] shows the whole of the Northern Hemisphere and the areas of dark blues and purples, (the Polar Vortex), that dominates some of it. If wanting a prolonged cold setup, you never want the Polar Vortex to be too invasive to the North-West of us, and especially over Greenland and Iceland, as it can make it hard for Northern blocking to form. The exceptions would be if a 'SSW', or other form of Stratospheric Warming, event occurs (and even then, it would have to be in the right place), or if we get some notable 'WAA' going up into Greenland or Iceland. (see 'Sudden Stratospheric Warming' and 'WAA' for more details). (There's probably likely to be other methods that I've admittedly not thought about, or know about, that could put the Polar Vortex under threat). Q R Retrogressing High - A High pressure system that backs away North-Westwards. For example, a High over the UK can sometimes retrogress towards Greenland. Whether a High retrogresses or not depends on various aspects such the dominance of the Polar Vortex (during Winter) and how obtrusive the Jet Stream is; if a powerful stream of the Jet is flowing over the top of the High, then it could have a hard time retrogressing (unless the main area of the Jet Stream suddenly heads South, or if the pattern significantly amplifies). It could also depend on other factors such as whether a Low Pressure system can pump up some 'Warm Air Advection' Northwards on the High Pressure system's Western side and help encourage heights to build further Northwards. Ridge / Ridging - A curvy or pointy area of a High Pressure system. It can be quite elongated. A High Pressure system will, at times, send some of its ridging from one area to another. This idea of 'ridging' means a High Pressure system is trying to extend its heights to other places. An example of a ridge of High Pressure: S Shortwave - It is essentially like a little Low Pressure system that hasn't quite become a proper closed-off circular Low (although they can sometimes develop into circular Low Pressure systems depending on the conditions within the atmosphere). Shortwaves are marked by a small(ish) curvy-shaped wave on the Pressure charts and are often a part of big Low Pressure systems and Longwave Troughs. Cold air above can also often be a part of Shortwave features. Some examples of shortwaves on the chart below (circled in black): Slack airflow - Where the isobars on the pressure charts are very spaced out. A slack airflow is associated by gentle winds, or a gentle breeze. Virtually, the weather is non-windy. Sudden Stratospheric Warming - 'SSW' may also be used. A sudden warming event occurs within the Stratosphere and, if notable enough, can separate the Polar Vortex (and its blue/purple blobs) into separate segments. Or even just make it less stronger in general. Where ever an 'SSW' event occurs, heights will likely to keenly rise in that area. As such, if you wanted a cold setup with a strong, sturdy, Greenland High, a notable 'SSW' event would be ideal around that area to help split the Polar Vortex in that area into two, with a segment of it getting knocked further West and with a segment of it being knocked Eastwards towards Scandinavia. In fact, getting a segment of the Polar Vortex to drop down to the North East of us can help promote Scandinavian Troughs and, if close enough, the UK can become influenced by a very cold Northerly flow from a Trough/Low over Scandinavia. T Trough - An area of curvy Low heights away from a main Low Pressure system's centre. Weather fronts and convective weather can be a part of troughs. Troughs are also a part of stretchy Low Pressure systems, and they can by quite pointy shaped. In the United Kingdom, a trough will be marked by a solid line on the Fax charts. There are, nevertheless, different kind of troughs such as Upper-Air Troughs, Surface Troughs, Shortwave Troughs and Longwave Troughs. The black circle on this chart shows an example of a trough tracking towards the UK: T+??? - To refer to a time-frame within the models. For example, 'T+48' would refer to a model outcome 48 hours ahead. U UKMO - A weather model owned by the UK Met Office. It has comparable performance to ECMWF, although this model can only be viewed up to 144 hours ahead. This model updates twice a day and is made up of the 00Z run and the 12Z run. Undercutting - When an approaching Low Pressure system out West tries to slide underneath a High Pressure system further East. Easterly winds can develop over the UK if the Low undercuts to the South of the island. The same could happen in any other country if a Low undercuts to the South of it. (850 hPa) Upper Temperatures - Can also be known as 'Upper Temperatures' or just 'Uppers'. They refer to the temperatures high up in the atmosphere (around 1,500 meters from the Earth's surface) and can be one of the factors that determine what the temperatures may be like at the surface. The warmer the 850 hPa temperatures are, the warmer the surface temperatures are likely to be. But this won't always necessarily be the case, as cloud, mist, or heavy rain can help to suppress the temperatures somewhat. Likewise, the colder the Upper Temperatures are, the colder the surface temperatures are likely to be, although again, certain weather scenarios can have an impact on this. In a sunshine and shower setup, you really need the uppers to be around -7*C or colder for snow to reach low levels. However, even uppers around -5*C can suffice if the shower is very heavy (encouraging Evapourative Cooling), and if surface temperatures near the ground are particularly cold with no real layer of warm air above. The Dam-line (the 500 - 1000 hPa Thickness) needs to be around 527 or lower, as well, for showers to fall as sleet or snow. But again, like with the uppers, you could get away with the Dam-line being a little higher if the showers are extremely heavy. For frontal bands of precipitation, you can get away with the uppers being as warm as 0*C and snow can still fall to low levels. This, nonetheless, is mostly true in situations where an Atlantic front is forced to bang up against High Pressure to the North (with Low Pressure to our South). The front then slowly pivots and gets pulled Westwards/North-Westwards through the UK via cold Easterly or South-Easterly winds. An example of an '850 hPa and Sea Level Pressure' chart below. The greens, blues and dark blues represent Upper Temperatures around 0*C or colder, while the yellows, oranges and reds represent uppers around 0*C or warmer. Helpfully, the Upper Temperature gradients are marked by black lines with numbers over the top of the lines to show how warm or cold the uppers are expected to be in that area. Over the far North of Scotland, for example, the 0*C Upper Temperature line crosses a part of it, with the -5*C Upper Temperature line crossing a part of Iceland further North-North-Westwards. You can also refer to the model's Upper Temperature colour-coding line to the right of the chart to work out how warm or cold the uppers are over your area. (However, if you have a Netweather Extra subscription, or are thinking about getting one, you can view the upper temperatures just for the UK only). V Vortex - Part of the Polar Vortex. W WAA - Warm Air Advection. This is where warm air from the South gets drawn up Northwards and moves into areas of cold air. In the Northern Hemisphere, the warm air would get drawn up on a Low Pressure system's Eastern side. When warm air gets 'advected' Northwards towards areas of cooler air, it can help strengthen High Pressure systems in that area, or even help new ones to form. This is why if you want a cold, blocked setup in Winter with High Pressure to our North or North-West, getting WAA heading up directly towards Greenland is seen as an encouraging sign. Below is an example from January 1947 of WAA being pumped Northwards: The example above shows a long drawn Southerly airflow to the West of the UK bringing warm air up from the South (shown by the red arrows). Mild Upper Temperatures are also brought Northwards (see the example below): Prolonged Northern blocking soon followed after this event in 1947, and the rest of that Winter was very cold. Weather Models - Charts, such as the ones you might be looking at right now, that display graphical weather forecasts and predictions, and use a large range of data. Their are a wide selection of weather models that all have varying purposes within our global Meteorological Weather operations. Satellites, radio equipment and weather balloons are used to detect the atmospheric and oceanic conditions on our planet, with special computers or super-computers working out all sorts of mathematical equations from the data that's gathered to then provide forecasts on various models. There are many different types of models, and various different model viewers in which you can view the charts from. In the UK, you can view charts that cover a portion of the Northern hemisphere, or the whole of the Northern hemisphere. Viewing versions of models that show the whole of the Northern hemisphere is highly recommended if you want to get a broader picture of how the pressure conditions and atmospheric conditions are behaving. The way one pressure system behaves on one side of the world can have impacts as to what happens in other areas of the globe. This is why viewing versions of charts that cover a broad area can be useful. Just one other thing to add is that you can also view historical charts dating to over 100 years back as well. WMA - Weather Model Addiction. Something some weather site member's are prone to catching. The addictions may include frequent model checking, frequent model analyzing and frequent viewing of the weather model threads across the World Wide Web. X Y Z Zonal Setup - The type of pattern that can bring about a North and South divide. On the whole, the Southern half of the UK remains settled with high pressure influential to the South, while the Northern part of the UK remains more cooler and unsettled with Low Pressure systems and Longwave troughs being more influential in those areas. Hence you begin to see why this is called a 'Zonal Setup'. Zonal patterns usually bring mild, or average conditions with a fairly long draw of winds from the West or South-West. However, not all Zonal setups bring mild or average temperatures. If winds come down from the North-West with High Pressure influential to the South-West of the UK and Low Pressure influential to the North/North-East, a cold Zonal setup can arise. Snow is also possible (if occurring in Winter), especially to the North and on high ground. ------------------------------------ Other useful information: Model Output Update Times (credit goes to Bottesford: http://forum.netweather.tv/topic/72242-model-output-update-times/) Model and chart viewers: [*]Netweather: http://www.netweather.tv/index.cgi?action=charts-and-data;sess= (The Netweather Extra section, where you can view more charts, is worth subscribing to) [*]The Weather Outlook: http://www.theweatheroutlook.com/twodata/datmdlout.aspx [*]Wetterzentrale: http://www.wetterzentrale.de/topkarten/fsavneur.html [*]Meteocial: http://www.meteociel.fr/modeles/ [*]WeatherCast: http://www.weathercast.co.uk/latest-model-forecasts/gfs-ncep.html [*]WeatherOnline: http://www.weatheronline.co.uk/cgi-bin/expertcharts [*]MeteoGroup: http://meteocentre.com/models/models.php?lang=en
  10. With the models under some degree of scrutiny I always forget which has higher resolution here and there and at what time frames. After some digging around put this together and hope it is some use as a point of reference, this is not my area of expertise so please edit, add to, correct, grow etc etc Data for numerical weather prediction is provided by observations from satellites, from the ground (both human and from automatic weather stations), from buoys at sea, radar, radiosonde weather baloons,, wind profilers, commercial aircraft and a background field from previous model runs. The gist of this is shown by this handy pic from a non-blacked out Wikipedia and ensembles depicted from UKMO website. UKMO Unified Model - Global Model 25Km Resolution 70 Vertical Levels 144 Hours UKMO North Atlantic and European Model NAE 12Km Resolution 70 Vertical Levels 48 Hours UKMO - Other 1.5km Resolution UK 70 Vertical Levels 36 Hours 4Km Resolution Surrounding Areas     ECM / IFS 16 /31km? unsure.. Operational / Deterministic run is Twice Hortizontal Resolution of Ensembles 240 Hours Operational 60 Vertical Levels Ensembles 40 Vertical Levels 51 member Ensemble suite http://www.ecmwf.int...techniques.html   GFS 35 km / 64 vertical layers High Resolution runs to 192 Hours / 7 days - every 3 hrs 70 km / 64 vertical layers Lower Resolution runs from 192 - 384 Hrs - every 12th hr 22 Ensemble Suite 9 including Control / Operational GEFS using current operational GFS -increase in horizontal resolution from 70 km to 55 km (T254) for 0-192 h, and 70 km (T190) for 192-394 hours -increase in vertical resolution from 28 to 42 layers for 0-384 hours http://www.emc.ncep..../GEFS/mconf.php
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