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Paul

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  1. A new model thread as we near a new season. Now we're out of the winter rush, we're onto a single model related thread again, so please keep it to the models in here. There's a fair bit of interest currently with some unusually mild air on the way later this week and into the weekend. Looks like temperatures records could be threatened, at least the daily and regional ones, the UK record of 19.7c seems quite unlikely at the moment. Beyond that, lots of uncertainty - take your pick from more of the same, a colder still mostly blocked picture or the return of the Atlantic - so plenty to be keeping an eye on as we end the winter. Thread Moderation The team will moderate this thread to keep it on topic and focused on the models. Please only post model related discussion. Alternate Threads If you want to chat about the winter in general, have a moan about it, or whatever else, there is a thread here for that: https://www.netweather.tv/forum/topic/91052-winter-weather-chat-moans-banter-and-ramps/ The Spring thread is also up and running: https://www.netweather.tv/forum/topic/91223-spring-2019-moans-ramps-chat-etc/ And for the Met Office outlooks, there's this thread: https://www.netweather.tv/forum/topic/64157-meto-uk-further-outlook/ Model Output And Charts On Netweather: GFS GFS FV3 (Para) GEFS Ensembles ECMWF ECMWF EPS NetWx-SR (3km) NetWx-MR (9km) Met-Office Fax GEM GFS Hourly Model Comparison Global Jet Stream Stratosphere
  2. A thread to let your hair down a bit, chat about all things winter weather, moan about it, ramp it up etc.
  3. 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/
  4. Sorry all, we may never get to the bottom of where the previous thread went unfortunately, but here's a fresh thread to get going with..
  5. 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.
  6. Please use this thread if you have any problems with the site or the forum, we will then do our best to help out..
  7. It will be (today) and has already been 7 or 8c+ warmer than usual for the time of year. What terminology would you use to describe the weather becoming cooler?
  8. Little doubting the direction of travel on the GEFS ensembles this morning, a distinct downward turn in temperatures. Aberdeen Derby London The pressure pattern tells a story too bringing lower pressure in, so cool/colder and less settled the likely outcome based on this run at least. Vs climatology it's also quite striking, starting at much warmer than normal before slowly edging cooler, to end the run much closer to, or below normal.
  9. Makes me wonder if they're experimenting with AI to write those bits.
  10. This is a sister thread to the looser Cold hunt - models and banter thread, and is a stricter, more focused and generally more in depth model discussion. Thread Moderation The team will moderate this thread to keep it on topic and focused on the models. Please only post model related discussion in here. You are welcome and encouraged to cross-post on this thread and the models/banter thread. Model Output And Charts On Netweather: GFS GFS FV3 (Para) GEFS Ensembles ECMWF ECMWF EPS NetWx-SR (3km) NetWx-MR (9km) Met-Office Fax GEM GFS Hourly Model Comparison Global Jet Stream Stratosphere
  11. After a lot of thought, we've decided to revisit the hunt for cold style thread, and this is it! In this thread, please feel free to discuss the model output with a cold slant, but should other weather types be showing in the output, discussing those is fine too. Thread Moderation The moderation in this thread will be on an impact basis, so if a post is likely to negatively impact the thread (by poisoning the atmosphere, creating lots of very off topic replies etc) then we'll moderate it. But for slightly off topic or bantery posts, we won't - so long as there is a general theme of the models running through the thread. This does mean that topics such as met office forecasts, tv forecasts, will it snow in my location type questions are still not allowed in this thread, as they are the types of things which will cause it to run off on a massive, non-model related tangent. Want a stricter, more focused model thread? As a sister-thread to this one, a focused, more in depth model thread is available. Please head to this thread for a slower paced, less bantery more strictly on-topic model discussion. Focused Model Discussion Cross-posting between this and the focused thread is allowed, and encouraged - so please feel free to post your thoughts, model run summaries and the like into both threads if you wish. We hope that these two threads offer the best of both worlds for everyone who want to follow and discuss the model output. Model Output And Charts On Netweather: GFS GFS FV3 (Para) GEFS Ensembles ECMWF ECMWF EPS NetWx-SR (3km) NetWx-MR (9km) Met-Office Fax GEM GFS Hourly Model Comparison Global Jet Stream Stratosphere
  12. Not this stuff again, please. The same people seem to get embroiled in the same stuff every year, why does it matter? Some people like warm weather, some like cold, end of discussion.
  13. Nick's take on the winter so far: Winter 2018/19: Sudden Stratospheric Warming - But Why No Beast From The East?
  14. I'll check our ad scanning is working properly as that sort of stuff shouldn't happen. But would recommend clearing your browser cookies/cache SS as it could be a local thing on your device.
  15. Ok, enough of the childish ott moaning in here, it's too much and is throwing the thread way off topic. Any more will be deleted, and persistent offenders with regard to this sort if thing will be stopped from posting in here.
  16. Lots of good analysis today in the focused thread: https://www.netweather.tv/forum/topic/91214-focussed-model-discussion/?page=15 Everyone is welcome to post their longer form thoughts on runs etc in there..
  17. It's models and banter (with the emphasis on models, this being a weather forum n all), so if the banter takes over, it ceases to be that. Just asking people to self-moderate a tad here, that's all..
  18. Folks, chill out a tad with the banter please, it's all well and good having the odd joke, but when someone says something bantery, is there really a need for 10 virtually identical attempts at the same joke? It just sends the thread way away from the models. There's a balance to be had here, so lets try to remember what the main point of the thread is.
  19. Just as a reminder for those wanting a slower-paced, less bantery model discussion, you can head over to the focused model thread here: As a suggestion to people wanting to get involved in there, but unsure what sort of thing to post - a great place to start may be to post a summary of your views on the latest model run (eg the GFS 12Z at this point), or maybe the suite of models up to this point today. They'll be good to read, and a good starting point for more discussions I'm sure 🙂
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