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Paul

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Everything posted by Paul

  1. Here we go with a fresh hunt for cold thread as we move into a colder spell of weather and towards the end of Autumn. As this is a new thread for this season, there's perhaps been a bit of confusion over what does or doesn't fit in here. So to help out, and be transparent in terms of our moderation of the thread, these are the guidelines we're working to, so if everyone can aim to stay within them, happy days! This is a model related thread, so a general, frequent theme of the model output is a given, but it will not be strictly enforced: Some topic drift, humorous responses etc are fine Posts likely to lead the thread off on an entirely off topic tangent are not ok. For example (but not solely limited to): Posts entirely or mainly about Met Office, BBC or media forecasts with little or no model context, and posts solely asking for a weather forecast in a specific location. Posts which start with something like 'I know this is off topic but ...' are not ok. Posts which break the forum guidelines are not ok (eg trolling, troll-hunting, weather guilt tripping, overly defensive/aggressive, abusive, disrespectful to others) Hopefully this helps, if in doubt please ask a member of the team, and if you see a post you think may fall outside of these guidelines, please report it. If you'd prefer a slower paced, more general (not cold slanted) model discussion, please head over to the general thread here. Model Output And Charts On Netweather: GFS GEFS Ensembles ECMWF ECMWF EPS NetWx-SR NetWx-MR Met-Office Fax GEM GFS Hourly Model Comparison Global Jet Stream Stratosphere
  2. A new thread as we move past the mid-point of Autumn.. This thread is for more general model discussion - eg without the specific focus on the hunt for cold weather, which can be found in the hunt for cold model thread. As ever, please keep it to the models in here. 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 Model Comparison Global Jet Stream Stratosphere
  3. 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.
  4. 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/
  5. 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..
  6. As mentioned at the top of this thread, there does need to be a frequent, general theme of model discussion across it, even if it's not super-strict in here. This evening it's gone too far the other way, and there's way too much banter and not enough discussion, so please consider what you're posting.
  7. This is a new thread option we're trialling, which hopefully will become a regular. Please use it to discuss the model output at short range (between 0 and 72 hours). For longer term discussion, please head over to the main model thread: 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 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 New Year!
  8. That's just because it's the para, the one hour timeframes will still be in the upgraded operational as far as I'm aware.
  9. Santa has been updated https://www.netweather.tv/weather-forecasts/uk/xmas
  10. Paul

    Introductions!

    If you're a new member and you would like to drop in and say hello, here's the thread to do it! Feel free to introduce yourself and ask any questions you may have, you'll find we're all a friendly bunch (apart from Oon, watch him!).
  11. With winter approaching over the horizon, a lot of people's thoughts are turning to cold weather potential, but while that's fine, it's not everyone's cup of tea. So, we've started this thread for the cold hunting side of model discussion, with a general discussion thread also up and running for those who'd rather look at all other aspects of the model output. Despite the focus on cold weather potential in this thread, please do keep it to the model output. 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 Model Comparison Global Jet Stream Stratosphere
  12. So, with the first few account restrictions in place as of this evening due to posts in here, now's maybe a good time to remind those who post the following sorts of things, your cards are marked.. Posting solely to generate negative/extreme reactions Over-reacting to model output/other peoples posts in such a way as to disrupt the thread Jumping all over and accusing people of trolling just because they don't agree with you/the consensus (please report people you think are trolling, don't respond - we will deal with it) Being ultra-defensive As a general rule of thumb, please just be nice - we're all here to enjoy discussing the weather.
  13. This must be at least the millionth time myself or others in the team have requested this, so it would be great if those who keep ignoring these requests could take it on board. Can we keep it to the models in here please, discussion solely about meto updates and the like with zero context around the models is not for this thread. There is a met office thread in the general weather area for that.
  14. @jethro - I suppose the immediate thing I take from your post is the question as to why this particular thread is in this part of the forum if it's unrelated to climate change/agw? My comments yesterday were more general about climate change discussions in here, not this subject in particular. If it's a weather subject, and people want to keep it away from the topic of climate change, then the obvious answer would be to have a thread in a weather related area, which is where all of this started up. Unfortunately, the topic didn't last long before it turned into an argument around agw etc, which ended up with it being locked and moved in here, so the rules were stricter. This is the problem, it's seemingly impossible to stop this type of thing turning in a circular argument, because frankly, there are too many with a pre-decided view about agw/climate change etc, that are entirely happy to ignore any and all evidence presented to them which disagrees with their view. We had to take a stand by making these discussions science only - yes that's limited the discussion in here, but when 90% of those discussions essentially turned into slanging matches anyway, what was the point in having them? Ultimately, it's a case of self-moderation vs site-moderation, if those involved could stop being so protective of their 'views' and open themselves up to debating without being defensive, even being prepared to change their minds in the light of evidence once in a while, then the issues resolve themselves. If that were the case, we could have threads like this in weather areas, and we could loosen the rules on debate on climate change in here too, but so far at least, that's not been the case. I'm not against this thread being open in 2 places, one weather, one climate, but it's down to the participants to not turn them into arguments.
  15. You can discuss it however you want in your own time etc, but in terms of the discussions on here, that's the way it is.
  16. No-one has said that, this from my post earlier: And as Pete says, providing some evidence to back up hunches or views is the way forwards to. Bringing no backup, and being unwilling to take evidence on board is what won't work.
  17. This is a science based forum area, and it's a science based subject, so it's not the place for those who want to ignore that side of things, I'm afraid.
  18. I'm confused, what you seem to be requesting @SteveB is a thread where people can disagree with proven science based on hunches and not have anyone present evidence which disproves that hunch? Why would that be a good thing? Why do you feel that you're being 'put down', when all that's happening is that you're presenting a view with no evidence, and those who have more knowledge are showing evidence which disagrees? At some point, when a mountain of evidence points in one direction, hunches backed up with nothing can't be given their own place to be discussed without any sort of evidence or science based elements to it. That's just a recipe to mislead those who want to learn, and an echo chamber for those who don't want science and evidence to get in the way of whatever it is they want to believe. Don't get me wrong, there's nothing wrong with asking questions, giving views etc based on hunches, and finding out whether there is any evidence to support those hunches, etc. But I don't think it's unreasonable to expect that, when presented with answers to questions, and science based evidence to back those answers up, that it's taken on board and accepted. Otherwise, you end up with a never ended circular debate where evidence apparently counts for nothing when it comes to some of the participants, and nothing good can come of that.
  19. Can we keep it to the models in here please, BBC forecasts and the like need to be posted about elsewhere.
  20. Although this thread is a bit more laid back in terms of having some banter, it does still need to be at least loosely model related, and at the moment some general winter and not model related comments are sneaking through. For those, please head over to the winter thread. https://www.netweather.tv/forum/topic/90634-winter-201819/
  21. Bearing in mind the forecast went as far as Monday/Tuesday, no further.
  22. For those following the upcoming switch to colder weather, Nick's latest blog is well worth a read. Colder Weather On The Way From The East Next Week, But Will It Snow? Jo's video from earlier is also well worth a watch:
  23. The Santa Shaker is back for another year https://www.netweather.tv/weather-forecasts/uk/xmas
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