Stratosphere watch 2019-20

sryanbruen

It is time for another crazy year of stratosphere watching yet again. I know this is quite unpopular after last year's SSW event that failed to propagate but the excitement lies in the journey in my opinion whether or not we do get a tropospheric response. Last year was fascinating from a stratospheric standpoint with a weak stratospheric polar vortex (SPV) during early autumn and record weak for a time in September (strengthened during November) to the SSW event during the New Year and then a big ramp up during February/March with daily records set for a strong SPV before a dramatic weakening for the final warming (FW) in April/May. I have illustrated each of these dynamic events on this MERRA2 graphic showing the daily zonal mean zonal winds at 60N 10hPa.



You can look at other years back to 1979 here for yourself if you so wish to.

For those that are new, the earth's atmosphere is divided into different layers. The troposphere is where weather occurs and the stratosphere is just above the troposphere. Much like the weather around the earth, the stratospheric temperature varies by season with it reaching its lowest point in December on average. Each autumn, a phenomena known as the stratospheric polar vortex forms within the Arctic Circle. This is an upper-level area of low pressure formed by the temperature difference between the equator and the pole. The vortex weakens and strengthens from year to year via dynamic events like stratospheric warming or the annual summer hibernation where the SPV "goes to sleep" due to a lower temperature gradient between the equator and the pole. The SPV is well defined when it's strong with a single vortex lying within the Arctic Circle.

Normally, the troposphere and stratosphere are in sync with each other which results in downwelling. This is when planetary waves are propagated to either level of the atmosphere via the weather patterns that occur. For example, an Aleutian Low (low pressure over or around Alaska) / Scandinavian High (high pressure over Scandinavia) combination can be a sign of disrupting the Polar Vortex and a precursor to a SSW event as a result. Another example is that with a cold stratosphere and healthy SPV, the North Atlantic jet stream is powered up bringing mild and moist conditions to western Europe with low pressure centred over Iceland. Tropospheric patterns that can have an impact on the SPV are defined by zonal wavenumbers which I would like to direct you to GL's excellent post from last year's thread here as I couldn't have explained it better myself.

There are different types of warming that occur and can have different degrees of impacts on the weather around the Northern Hemisphere if a tropospheric response occurs.

There is a minor stratospheric warming which involves the stratospheric temperature rising but less dramatically compared to a major warming and the zonal mean zonal winds do not reverse.

A major sudden stratospheric warming involves the zonal mean zonal winds at 60N 10hPa in the stratosphere to reverse from westerly to easterly. The SPV is completely disrupted and it will either be split into two or more vortices OR displaced from its normal location over the North Pole. Major SSW events are forced by tropospheric patterns disturbing the SPV but sometimes, these events can propagate back down into the troposphere and result in anomalously blocked patterns which gives a higher chance of colder weather for Europe. However, even if a SSW downwells successfully into the troposphere, the positioning of the blocking is a factor to consider also.

Cohen and Jones (2011) did a good paper on tropospheric precursors and categorising past SSW events into splits and displacements here, it's free access to everybody.

Met Éireann highlighted previous Irish cold spells and if a SSW could have caused them in their Storm Emma paper here.

Other warming events that occur include final warming events which indicate the transition into stratospheric summer hibernation mode and Canadian warming events which occur earlier in the winter.

Now with all that behind us, let's get on to the here, now and foreseeable future.

Currently, the forecast is for a readily strengthening SPV as zonal mean zonal winds at 60N 10hPa reach near record highs by this time next week on the GFS for the past few days. This should be an indication of a strong westerly flow across the North Atlantic but as it is right now, the troposphere and stratosphere are not in sync with one another as shown by the second chart below which shows the observed NAM (another name for the Arctic Oscillation basically) at different layers of the stratosphere with the troposphere at the bottom. The forecast after 1 November is by the GFS and it shows positive NAM within the stratosphere failing to downwell to the troposphere and the troposphere remains with negative NAM throughout the outlook. However, it's worth nothing that an earlier run of the GFS had the trop and strat coupling up with one another at the end of FI so even stratospheric forecasts are prone to wild changes on model runs as much as our own weather!

There is a minor warming on the latest GFS runs in FI associated with this negative NAM which forces a drop in the zonal mean zonal winds but I mean a drop from the record or near record levels is to be expected really. Nothing unusual here as far as I can see.





You can view updates on the NAM here.

Also always watch out for Cohen's Arctic Oscillation and Polar Vortex analysis updates: https://www.aer.com/science-research/climate-weather/arctic-oscillation/

To summarise for the reliable timeframe, the stratosphere is colder than average right now and is expected to get even colder as we progress through the first two weeks of November 2019. This results in a healthy stratospheric polar vortex but with the troposphere and stratosphere out of sync with one another, this does not look like downwelling any time soon to affect our weather patterns with the AO/NAO likely to remain either at negative or close to negative so blocking around the pole and the North Atlantic increasing the risk of colder than average conditions.

hatrickpatrick

Thanks as always for the incredibly informative refresher, Sryan :cool: I don't know about anyone else, but I haven't lost faith or interest in the strat despite last Winter's downwelling hiccup - that's the weather for you! Looking forward to seeing what happens this year and even just the possibility of seeing effects on our weather on the ground.

hatrickpatrick

The GFS has been very consistent in seeing the faint rumblings of a developing Strat warming towards the end of FI for the last couple of days. What effect if any that would have on tropospheric weather given the recent disconnects between the two is a bit of an open question, but it's certainly interesting to see charts like these showing up so early in the season, and sticking around for multiple days of model runs - in fact, the earliest appearance of a -20 isotherm has actually moved closer, from November 19th on yesterday's 18Z to November 15th on today's, and the earliest appearances of warmer isotherms has been similarly brought forward by tonight's run compared with last night's.

Usual caveats about FI charts apply, but looking back through the archives, I can't find a single example going back as far as 2013 (when Meteociel first began hosting Strat temperature charts) of significant warming showing up this early in the season.

Night gathers, and so our watch begins

Villain

The GFS continues with the warming towards the end of the run.

hatrickpatrick

We're back to the usual repeated pushing forward of the warming from run to run, I wouldn't get excited until these charts start moving closer on the models without fizzling out.

sryanbruen

Latest GEFS shows an impressive deceleration in the zonal mean zonal winds at 60N 10hPa going from record strong to near record weak with some ensembles (still quite the drop with the ensemble mean). This is incredible in November I must say and is a sign that the troposphere will really attempt to disturb the stratospheric Polar Vortex.

Yet again still no signal of the troposphere and stratosphere reconnecting in the outer reaches of Fantasy Island.



ECM sees a similar deceleration but maybe not as dramatic.

Captain Snow

bazlers

Captain Snow wrote: »

Fingers crossed captain snow. Although we may have have heard this once or twice before ; )

Captain Snow

bazlers wrote: »

Fingers crossed captain snow. Although we may have have heard this once or twice before ; )

Its been a strange synoptic set up for November. Anything can happen.

sryanbruen

It’s *quite* unusual that all this blocking is tropospheric driven in the high latitudes rather than being driven by the stratosphere. From research, I can spot only a few years that involved tropospheric driven blocking including 2009/10, 2010 and 1985/86. Various factors could be resulting in this including low solar forcing, North Atlantic SSTs and the descent of the easterly QBO that is ongoing etc.

hatrickpatrick

NAO is on the way down as well towards the end of the month if these forecasts hold :cool:



@Sryan, I could have sworn that 2010 was in fact an SSW-driven event? There aren't easily accessible strat charts going back that far so I'm going from memory here, could be wrong?

Captain Snow

sryanbruen wrote: »

It’s *quite* unusual that all this blocking is tropospheric driven in the high latitudes rather than being driven by the stratosphere. From research, I can spot only a few years that involved tropospheric driven blocking including 2009/10, 2010 and 1985/86. Various factors could be resulting in this including low solar forcing, North Atlantic SSTs and the descent of the easterly QBO that is ongoing etc.

How much influence would a Tripole help are set up? Probably helping HP anchor over central parts of the Atlantic?

We have a similar SST set up now like 2009 2010 currently. Wonder if that's a sign.

sryanbruen

hatrickpatrick wrote: »

NAO is on the way down as well towards the end of the month if these forecasts hold :cool:

@Sryan, I could have sworn that 2010 was in fact an SSW-driven event? There aren't easily accessible strat charts going back that far so I'm going from memory here, could be wrong?

Whilst we don't have a NAM chart to compare, here is the archive chart for zonal mean zonal winds at 60N 10hPa during Winter 2010/11 from weatheriscool.com. Besides a minor warming in early November 2010 and again in early January 2011, there was no major SSW during Winter 2010-11 - the February down spike is an error in the plotting although it doesn't quite reach reverse level anyway and the April down spike is the annual final warming.

You can see that comparing the blue line (2010-11) and black line (average), the zonal mean zonal winds at 60N 10hPa were largely above average during November and December 2010 in contrast to the extreme levels of high latitude blocking within the tropospheric layer.



There's no doubt in my mind that the textbook tripole in 2010 more than helped cause the extreme blocked patterns along with high amplification from a strong La Nina that was ongoing (although this would later result in a very mild February that same winter).

sryanbruen

Captain Snow wrote: »

How much influence would a Tripole help are set up? Probably helping HP anchor over central parts of the Atlantic?

We have a similar SST set up now like 2009 2010 currently. Wonder if that's a sign.

In my opinion, North Atlantic SSTs play a huge role in the North Atlantic Oscillation that not many realise or forget about. Last year, they supported a positive NAO and was the "spanner in the works" against the long range modelling that showed a big blocking feature to develop to our north during 2018-19... but as we saw, it was indeed another positive NAO winter which the North Atlantic SSTs during 2018 supported.

The current SST set up is similar to 2009 more than 2010 as in 2010, we had a classic example of a tripole. To get a tripole of such, there has to be three distinct bands of warm-cold-warm stretching from Greenland to the tropics with the cold especially over towards America. Not sure why this is the case (even after reading previous UK Met Office winter forecasts from like 2005-06 when they explained their methodology) but one theory I had was that the way nor'easters form in the eastern seaboard and come into contact with the relatively warm North Atlantic SSTs normally, they intensify the jet stream. However, with this part of the Atlantic cold, there is less of a temperature contrast so nor'easters or storms not as strong and more likely to go on a southerly track with a weak or meridional jet stream.

Birdnuts

sryanbruen wrote: »

In my opinion, North Atlantic SSTs play a huge role in the North Atlantic Oscillation that not many realise or forget about. Last year, they supported a positive NAO and was the "spanner in the works" against the long range modelling that showed a big blocking feature to develop to our north during 2018-19... but as we saw, it was indeed another positive NAO winter which the North Atlantic SSTs during 2018 supported.

The current SST set up is similar to 2009 more than 2010 as in 2010, we had a classic example of a tripole. To get a tripole of such, there has to be three distinct bands of warm-cold-warm stretching from Greenland to the tropics with the cold especially over towards America. Not sure why this is the case (even after reading previous UK Met Office winter forecasts from like 2005-06 when they explained their methodology) but one theory I had was that the way nor'easters form in the eastern seaboard and come into contact with the relatively warm North Atlantic SSTs normally, they intensify the jet stream. However, with this part of the Atlantic cold, there is less of a temperature contrast so nor'easters or storms not as strong and more likely to go on a southerly track with a weak or meridional jet stream.

Sounds like MT's winter forecast could be on the money!!

sryanbruen

The November update of the ECM is now suggesting a weaker than average stratospheric polar vortex at 10hPa during December 2019 contrast to last month's update. However, the Glosea5 is less confident on this with quite a high spread especially in January. It's important to note that the Glosea5 has a better verification record than the seasonal ECM but at the end of the day, they're long range models so prone to huge changes.

https://twitter.com/SimonLeeWx/status/1194962609595768833

Yesterday's GFS backed away significantly from the SPV getting disturbed with +AO filtering down through the atmosphere in FI whilst still forecasting quite a weakening in the zonal mean zonal winds at 60N 10hPa. The ECM showed similar but actually also showed a strengthening again at the end of FI.

Very confusing picture.

Villain

End of GFS run this morning

Villain

Winds forecast today, starting to see what could be the start of some foundations being poured?

Gonzo

It's certainly early to be seeing one of these, lets see how it plays out, last winter it didn't play in our favour.

hatrickpatrick

Someone with more knowledge of the modelling data might be able to shed some light on this: A poster over at NetWeather mentioned that since November 15th, the GFS and its ensembles have been running without one of its datasets, the Ozone Monitoring Instrument (OMI) and that this can result in a warm bias in the strat charts. That poster reckoned that the warming we're seeing was still most likely legit, but that it might appear stronger on the models runs until the OMI is reinstated.

I've had a quick look around online and can't find any information on this, or how soon this data might be reintroduced into the GFS, anyone have any further info?

aidanodr

UK weather forecast: Terrifying map shows COLLAPSED polar vortex freezing UK in December - DE EXPREZZZZZ

highdef

aidanodr wrote: »

UK weather forecast: Terrifying map shows COLLAPSED polar vortex freezing UK in December - DE EXPREZZZZZ

Warning..... This link is to a ****ty British tabloid newspaper well known for over hyping the weather.

Oneiric 3

aidanodr wrote: »

UK weather forecast: Terrifying map shows COLLAPSED polar vortex freezing UK in December - DE EXPREZZZZZ

hatrickpatrick

highdef wrote: »

Warning..... This link is to a ****ty British tabloid newspaper well known for over hyping the weather.

They over hype everything. I've been waiting ten years for the imminent apocalyptic Yellowstone eruption they were talking about back in 2008

Villain

0c be warm

Villain

Latest GFS

BLIZZARD7

Looking good for a PV disruption mid December me thinks... Could be timed perfectly as the trop/pv reconnects just in time to be disrupted.

Gaoth Laidir

The ECMWF had a big seminar on the stratosphere recently.

https://www.ecmwf.int/en/about/media-centre/news/2019/scientists-review-impact-stratosphere-weather

There are also some known issues with ECMWF’s model at the sub-seasonal to seasonal range.

“There are stratospheric temperature biases in the model, and the connection between the troposphere and the stratosphere becomes too weak in the northern hemisphere beyond a month into the forecast,” says ECMWF scientist Tim Stockdale, who co-organised the event.

Tim Stockdale talked about a new approach to linear ozone modelling.

Recommendations made at the workshop include improved modelling of gravity waves (atmospheric waves produced, for example, by airflow over mountains) and of the mesosphere (the atmospheric layer above the stratosphere).

Tim points out that a snap poll among the attending scientists showed little consensus, and a great deal of uncertainty, about the correct seasonal forecast for this winter.

“It illustrates the fact that seasonal winter forecasts for Europe are difficult. It means that we have our work cut out to improve our models, and the findings presented at this workshop will help us to move forward.”

Gonzo

not what we want to see seeing going into December.

nacho libre

Judah Cohen seems to suggest there maybe a Canadian warming going on.


"But since late November the Ural/Scandinavian blocking has been replaced by much lower pressures/heights (probably in part to the migration of the PV center to that region), a pattern less favorable for disrupting the PV.

The models in general have been less aggressive in disrupting the PV and probably a major mid-winter warming (reversal of the zonal mean zonal wind from westerly or positive to easterly or negative at 60°N and 10 hPa) is less likely than I previously thought. All models predict a minor warming with ridging near Alaska and Northern Canada and the PV near and along the north slope of Eurasia. This does resemble what is referred to as a Canadian warming. This rarely results in a major warming but I do believe can be a precursor to a more significant warming later on. "

There was i believe a Canadian warming in some notable winters of the past

sryanbruen

Yeah, there looks to be some kind of warming at 10hPa to the north of Canada whilst the SPV is displaced somewhat from its normal position to Eurasia. However, the forecast is for a strengthening again of the SPV after this temporary weakening and minor warming that is ongoing right now.

For clarity, proper Canadian Warming events have occurred in Nov 1951, Nov 1952, Dec 1954, Nov 1958, Dec 1958, Dec 1959, Nov 1962, Dec 1965, Dec 1966, Nov 1968, Nov 1972, Nov 1974, Nov 1976, Nov 1977, Dec 1978, Nov 1979, Nov 1980, Dec 1981, Nov 1991, Dec 1993, Nov 1996 and Nov 2000.

sryanbruen

sryanbruen wrote: »

It’s *quite* unusual that all this blocking is tropospheric driven in the high latitudes rather than being driven by the stratosphere. From research, I can spot only a few years that involved tropospheric driven blocking including 2009/10, 2010 and 1985/86. Various factors could be resulting in this including low solar forcing, North Atlantic SSTs and the descent of the easterly QBO that is ongoing etc.

In the space of just over a month, the outlook could not be any more different to what this post would suggest from mid-November. The deceleration in the zonal mean zonal winds did verify at the beginning of December but we have since seen a ramp up (which the GEFS did not forecast) and currently the zonal mean zonal winds are above average though we are nearing the climatological peak anyway. It should be noted that the GEFS (which are of the old legacy GFS and haven't been upgraded unlike the FV3 but are set to get an upgrade in 2020) frequently diverged with the GFS operational run. They frequently suggested a weak to very weak stratospheric polar vortex for mid-December whilst the operational was generally on the other side but even it did not foresee the ramp up that has occurred. Simon's tweet below illustrates this perfectly. Shows how even the stratosphere forecasts have to be taken with a large pinch of salt much like our own forecasts.

https://twitter.com/SimonLeeWx/status/1206888324247511040



The Arctic Oscillation for the foreseeable future is set to be positive so a strong polar vortex is to be penciled in over the Arctic. Literally no sign of it being disturbed. Tropospheric patterns look unfavourable too with a flat westerly flow across the Northern Hemisphere.

BLIZZARD7

Some signs of a SSW appearing now in the models - Winter to appear late February? Mid February possible with a QTR but Late Feb/Early march if it's the normal ~ 3 week lag impact.

Assuming we even get there...

A few GEFS members showing a reversal -

sryanbruen

More GFS members including the operational have gone towards a technical SSW this morning and some even show evidence of a little PV split right at the very end of their runs. Ultimate Fantasy Island and as we’ve seen this winter, stratospheric forecasting can be as unreliable as our own 7-10 day timeframe forecasts but we’ll keep watching.

I think ECM was showing a wave-1 displacement yesterday too with the PV displaced to Eurasia. Let’s see what it shows later today.

Billcarson

If we do get a ssw,would I be right in saying 2 things in our favour this yr compared to last yrs ssw is that the qbo is now in its easterly phase and also the fact that the ssw would be happening later then last yr . In Feb the pv should be weaking naturally a bit anyway.

Mortelaro

I'll just stick this here will I

https://twitter.com/Petagna/status/1221095773309427712?s=19

sryanbruen

Thanks BB. Marco also posted the ECM 0z output for the strat (which hasn't updated on the Berlin website where I usually get my ECM charts from) and it does show almost a SPV split at the very end of its run with two areas of warmer than average temperatures (North Pacific and northern Europe) attempting to split the vortex into two or more vortices.

Meanwhile, GFS 12z backed away from the split to the very end of its run too at day 16 rather than days 13-14 which it showed on previous runs but the displacement is still at large shown and getting closer any day now. As ever... more runs needed and days to progress.

https://twitter.com/Petagna/status/1221098767438446593

Billcarson wrote: »

If we do get a ssw,would I be right in saying 2 things in our favour this yr compared to last yrs ssw is that the qbo is now in its easterly phase and also the fact that the ssw would be happening later then last yr . In Feb the pv should be weaking naturally a bit anyway.

I don't rate the QBO too highly so I wouldn't know much about that but I think it would be fair to say that the later occurrence of this SSW (if it were to verify) would have more of an impact compared to last year's event. Last year's event was also succeeded by a big swave of westerlies in the stratosphere which resulted in record-breaking daily zonal mean zonal winds and it coincided with the westerly QBO growing in amplitude. It's the exact opposite this year... this expected stratospheric warming event follows on from record breaking SPV conditions and a weakening westerly QBO as the easterly QBO descends from the top of the atmosphere.

Remember every SSW event is unique.

Billcarson

Was the main problem with last yrs ssw that there wasnt enough downwelling? I presume the ssw of Feb 2018 was more textbook even though as you say every ssw is different.

sryanbruen

More steps back this morning from the GFS with a fair weakening of the SPV forecast but no major SSW bar a few ensemble members that are clear outliers. Displacement still in the forecast but does not cause any reversal although remember it doesn’t have to be a reversal for impacts to be felt on the troposphere. Splits are better for quick tropospheric responses as well as for more prolonged cold patterns.

These are the games you have to play with Fantasy Island. As for my own opinion, I do not see a major SSW this winter. I have no reason to think there will be. There is a lack of global patterns that would support a major disruption to the SPV.

sryanbruen

10 hPa stratospheric temperatures have returned to average or slightly above average for the first time this winter since the early days of December.



An uptick at 30 hPa too but yet to return to average.



https://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/index.html

nacho libre

sryanbruen wrote: »

10 hPa stratospheric temperatures have returned to average or slightly above average for the first time this winter since the early days of December.



An uptick at 30 hPa too but yet to return to average.



https://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/index.html

Is this just part of the natural occurrence at this time of year? Can you recall any notable wintry events in recent times from a vortex displacement?

Kermit.de.frog

Given the time it takes for warming at 10hpa to propagate down through the layers of the atmosphere even if an unusually steep rise in temperatures occurred right now you'd be lucky to see the practical effects on surface level pressure patterns by the end of February. The lag is weeks.

Even then it is no guarantee of cold weather in any case.

Missed the boat this year.

All we can hope for is to sneak something out of a slowing of the zonal pattern. More traditional route but not as spectacular.

sryanbruen

Billcarson wrote: »

Was the main problem with last yrs ssw that there wasnt enough downwelling? I presume the ssw of Feb 2018 was more textbook even though as you say every ssw is different.

Yes, it failed to downwell so there was a lack of -NAM and in fact, it went very positive in February at the same time that there was a big ramp up in the zonal mean zonal winds.

The February 2018 SSW was abrupt and perfect to developing a Beast from the East type setup as the initial warming occurred over Siberia (this allowed a Siberian High to develop once downwelling was successful) and then we saw a secondary warming around Greenland a few days later which resulted in a split of the SPV. The vortices were placed to the west of America and southeast Europe.

We saw the first signs of downwelling very quickly by the 22nd (10 days after the initial date of the major SSW event) when an anticyclone was evolving to the north and northeast of Scandinavia before becoming an actual Scandinavia High. There was warm air advection in the North Atlantic despite the vortex around Greenland which allowed the high to boost and an exceptionally cold airmass push around the high into Russia and then eventually Europe before reaching us by the 26th and 27th. All the building blocks were in place as they say.



There were some Scandinavian Highs in November and December 2018 that would have likely resulted in the major SSW event in late Dec/early Jan but as mentioned, there was no downwelling and was the first nSSW (non-propagating classified) since February 2008. As some strat experts mentioned, the run of successfully downwelling (also classified as dSSW events), PV split major SSW events of January 2009, February 2010, January 2013 and February 2018 was highly unusual.

I should mention that according to a study by Karpechko et al in early 2017 in the link below, though not publicly accessible, entitled "Predictability of downward propagation of major sudden stratospheric warmings", we could have anticipated the 2018/19 major SSW failing to downwell based on wave activity propagation to the stratosphere during the days immediately following the central or initial date of the dynamic event.

https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/qj.3017

This is a good figure showing past major SSW events classified as dSSW (propagating) and nSSW (non-propagating) from the paper. 2018 and 2019 not here because it was released in 2017 but we know that 2018 was a dSSW and 2019 was a nSSW.

nacho libre wrote: »

Is this just part of the natural occurrence at this time of year? Can you recall any notable wintry events in recent times from a vortex displacement?

Displacements are nothing unusual and frequently occur with minor SSW events (which is where the zonal mean zonal winds at 60N 10hPa do not reverse) which happen a few times on average every winter although this winter, this one will be the first since early December or late November as mentioned.

I'd say there have been a fair few but it'd be tedious to go through every example and take a good bit of time since they're not classified. In terms of major SSW events associated with displacements, the only one of note I can see that downwelled was that of early December 1981 which was immediately followed by the coldest December of the 20th century and a severe cold spell in January that everybody knows. The NAM wasn't persistently negative either which I'd expect with a displaced vortex.

Kermit.de.frog wrote: »

Given the time it takes for warming at 10hpa to propagate down through the layers of the atmosphere even if an unusually steep rise in temperatures occurred right now you'd be lucky to see the practical effects on surface level pressure patterns by the end of February. The lag is weeks.

Even then it is no guarantee of cold weather in any case.

Missed the boat this year.

All we can hope for is to sneak something out of a slowing of the zonal pattern. More traditional route but not as spectacular.

Depends on the type of event and the state of the atmosphere at the time. Some events can have very quick tropospheric responses like the 2018 one but these tend to be associated with splits rather than displacements. The split signal is almost pretty much vanished now from models with the GFS continuing to backtrack.

The displacement of the stratospheric polar vortex into eastern Europe *could* allow for some height rises close to the northwest if some propagation takes place. It's always "woulds" and "coulds" or "ifs" and "buts" with the weather of course.

sryanbruen

The minor warming only got the zonal mean zonal winds back to or slightly below the climatological average and now models forecast a big strengthening again with more record strong date records possibly. This is at a time when they should be weakening naturally too. Similar timing to last year's strong Polar Vortex/cold strat event in Feb/Mar but this looks stronger than that right now.

nacho libre

sryanbruen wrote: »

The minor warming only got the zonal mean zonal winds back to or slightly below the climatological average and now models forecast a big strengthening again with more record strong date records possibly. This is at a time when they should be weakening naturally too. Similar timing to last year's strong Polar Vortex/cold strat event in Feb/Mar but this looks stronger than that right now.

so the recent modelling of a Scandi High in fi on the GFS will be shortlived. With this upcoming cold spell, it shows a strong pv can be to our advantage sometimes/

sryanbruen

This Polar Vortex doesn't give it a rest.



GFS forecasting another wave of anomalous positive AO to propagate close to the troposphere in the foreseeable future but staying around the lower strat on this particular forecast. Nevertheless, no end in sight to the zonal westerlies!



Remember that this is, climatologically speaking, usually the time of year of the weakening phase of the Polar Vortex. Mean date for the Polar Vortex to go into summer hibernation is April 15th with extreme examples as early as near the start of March (2016) and as late as near mid-May (1981). We could be waiting a while yet.

This 2019-20 season is a real turn up for the books with its relentlessly strong Polar Vortex.

PukkaStukka

sryanbruen wrote: »

Mean date for the Polar Vortex to go into summer hibernation is April 15th with extreme examples as early as near the start of March (2016) and as late as near mid-May (1981). We could be waiting a while yet.

What is the impact on or implications for summer weather if the hibernation is considerably later than the mean?