Stratosphere and Polar Vortex Watch 2020

[jcw]

7 minutes ago, Snow lover 2020 said:

No an SSW has been talked about last few days. Where have you been? Lol it develops end of December 

Unfortunately talking about an SSW doesn't make it happen.

Useful to keep an eye on charts like this to see if there's any hint of a warming ahead...

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/gif/pole30_nh.gif

[Yarmy]

10 minutes ago, Snow lover 2020 said:

No an SSW has been talked about last few days. Where have you been? Lol it develops end of December 

This is what we have forecast at T330:

 

This is an SSW:

 

Besides, an SSW doesn't guarantee snow here anyway. If it did, we'd be buried every couple of years or so.

[Snow lover 2020]

14 minutes ago, Yarmy said:

This is what we have forecast at T330:

 

This is an SSW:

 

Besides, an SSW doesn't guarantee snow here anyway. If it did, we'd be buried every couple of years or so.

Yes 

 

18 minutes ago, jcw said:

Unfortunately talking about an SSW doesn't make it happen.

Useful to keep an eye on charts like this to see if there's any hint of a warming ahead...

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/gif/pole30_nh.gif

No there was actual charts based on it from various people on here and in the weather community on Twitter it “COULD” happen at end of Dec heading into a major SSW.  signs were pointing towards it if we get further blocking etc 

 

[Snow lover 2020]

1 hour ago, feb1991blizzard said:

More likely in mid to late Jan or even feb from where i ia coming from.

Ahhh well fingers crossed. 

[Catacol]

1 hour ago, feb1991blizzard said:

More likely in mid to late Jan or even feb from where i ia coming from.

Agreed. I'm watching troposheric patterns carefully now as precursor patterns do seem to me to be embedding and we also have surprisingly high momentum surges ongoing with consequent wave break potential and impacts. Things need to align...but from mid Dec onwards we might just see the first signs of vortex stress. Even the bias moderated charts are seeing something happening in January and while nothing is ever certain I'm hopeful that we can see an SSW this season to set up something more akin to real winter in late Jan and into February. Nina seems to be fading faster than I feared might happen which is good, and increasingly looking more like an EP rather than CP or mixed event. Funny isnt it....everyone seeing a front loaded winter and in fact it may pan out to work in reverse. Rarely do things in weather go to plan....!

For now - ebb and flow of a wavy pattern. Nothing much to see yet though it is interesting to note just how strongly embedded this ScEuro high seems to be. Short term frustration for long term pot of gold in some shape or form?

[feb1991blizzard]

1 minute ago, Catacol said:

Agreed. I'm watching troposheric patterns carefully now as precursor patterns do seem to me to be embedding and we also have surprisingly high momentum surges ongoing with consequent wave break potential and impacts. Things need to align...but from mid Dec onwards we might just see the first signs of vortex stress. Even the bias moderated charts are seeing something happening in January and while nothing is ever certain I'm hopeful that we can see an SSW this season to set up something more akin to real winter in late Jan and into February. Nina seems to be fading faster than I feared might happen which is good, and increasingly looking more like an EP rather than CP or mixed event. Funny isnt it....everyone seeing a front loaded winter and in fact it may pan out to work in reverse. Rarely do things in weather go to plan....!

For now - ebb and flow of a wavy pattern. Nothing much to see yet though it is interesting to note just how strongly embedded this ScEuro high seems to be. Short term frustration for long term pot of gold in some shape or form?

Yes - must admit i am slowly coming around to a 'winter of 2 halves type forecast' , as even a warm PDO would be surely negated somewhat in the Atlantic by the SST's re-calibrating by Feb so as to limit the effects, as the wavelength pattern might become more stationary, even a west based -NAO more possible then.

[DavidS]

The current uncorrected and bias corrected CFS . Obviously these can and do change significantly on a run to run basis. But nevertheless, the indication is there for a significant reduction 

[Blessed Weather]

A few of you may have spotted the tweet by Anthony Masiello yesterday describing how the anticyclonic wave break over Scandinavia/Barents teams up with the Aleutian Low pattern to squeeze the SPV. I thought it might be interesting to expand on the tweet with a broader look at what's happening.

Source: Twitter @antmasiello

So starting down at 500hPa where the GFS NH forecast (6z 30 Nov) for 1st Dec shows the combo of strong Aleution Low coming up against a strong Alaskan ridge and firing WAA polewards. Meanwhile over on the Atlantic side a similar process is taking place.

Next a look at the GFS 1.5 PVU (potential vorticity unit) chart for the same time shows the resultant 'wave' impact on the dynamic troposphere - the transition zone between the upper troposphere and the lower stratosphere. Where the boundary lies can vary in height from around 5.5 miles up to 11 miles and this fluctuates depending on factors such as the amplitude of weather disturbances below it and variances in the potential temperature gradient. Rossby waves can appear as undulations of these gradients. Here are the charts for 1st to the 3rd of Dec:

Next a look at the geopotential height anomalies, first working up from 250hPa up to 30hPa and showing the impact up through the levels. 

And then in the final chart in the sequence the impact at 10hPa (i.e. the SPV) and you can see the vortex has been stretched with two separate lobes detectable. 

Here's confirmation of the Wave 2 activity, but also confirmation that the amplitude is insufficient to causes too much of a problem to the vortex on this occasion, which became stretched, but not split:

Finally, confirmation that on this occasion the vortex soon shrugged off the attack, with a short lived drop in the zonal mean zonal winds which quickly recover:

Sources of charts: Meteociel and Weatheriscool.

[damianslaw]

8 hours ago, Yarmy said:

This is what we have forecast at T330:

 

This is an SSW:

 

Besides, an SSW doesn't guarantee snow here anyway. If it did, we'd be buried every couple of years or so.

Would be good to have one as happened in 2013, early Jan with quick effects, mid Jan cold snowy spell and long-term implications for rest of the winter. As said though SSW events don't always result in cold snowy weather here. 2019 a good example. 2009 and 2018 did have an impact though, 2009 was very quick response, 2018 much slower.

[bluearmy]

Gfs 12z got quite toasty right up at the top by the end of the run ....

[Mike Poole]

For the first time today i get a sense from some of the ensemble members of the brakes being put on the strat vortex, here’s the GEFS and GEM ensembles from Stratobserve:

Up until now I haven’t really spotted anything below 40 m/s, but GEFS have some in the 20s and GEM (CMC) have a couple in single figures.  One to watch.

[Allseasons-Si]

@Mike Poole,thanks for that^

The gfs/p from this morning perturbs the vortex somewhat,the gfs 12z kind of tries to get some warming going.

it will be interesting to see what happens as we tick along this month.

[mb018538]

Wouldn't want to go skiing on that downward slope!

[Snow lover 2020]

47 minutes ago, mb018538 said:

Wouldn't want to go skiing on that downward slope!

What does this chart mean 

[Catacol]

4 minutes ago, Snow lover 2020 said:

What does this chart mean 

Vortex weakening. Probably the impact of the wave 2 forcing I described yesterday. In general terms weaker vortex = greater chance of blocking patterns taking hold which helps break cold air out of the arctic and into lower latitudes. But note “chance”. Not the same as “Snow nirvana is on its way!”

[Blessed Weather]

1 hour ago, Snow lover 2020 said:

What does this chart mean 

In literal terms it's showing the speed of the winds spinning around the vortex way up at 10hPa in the stratosphere. The dark line is the long term average of what speed is normal at the point in time on the chart. The red line obviously the recent forecast wind speed. Positive numbers mean it's a westerly wind, negative numbers a reversal of the vortex into easterly winds. Dipping below zero signifies a SSW. A good introductory read on the NASA website:

Nasa Ozone Watch: Polar vortex facts

OZONEWATCH.GSFC.NASA.GOV

---

Polar vortex facts

 

[Kirkcaldy Weather]

GEFS continue to show stress / pressure being put on the vortex as we go through December, within the last few runs some attempting to get a fair amount of warmth going 
And just a question for the more experienced Stratosticians @Catacol  etc, I take it the wave 2 is when u see the warming from both sides ie similar to this one (tho the North American side isn’t really warm on that but just to illustrate my question ) ?  But we can still get split events from wave one events I think the Christmas warming in 2018 was a wave one? 
thanks in advance

 

[Mike Poole]

I guess there is concern that the strat vortex is bound to imprint on the trop vortex at some point and the result will be weeks of mild wet and windy weather for the UK.  But what if the opposite happened?

Plot shows the Northern Annular Mode timeseries at all levels of the atmosphere, the end of the forecast period is intriguing (from GFS 0z run).

[summer blizzard]

Upwellings are pretty rare to that degree, possibly 09 being an example.

Dec 18 saw wave 1 thump the vortex before a wave 2 finally produced the SSW a few days into January.

[Blessed Weather]

8 hours ago, Kirkcaldy Weather said:

GEFS continue to show stress / pressure being put on the vortex as we go through December..........

(SNIPPED)
And just a question for the more experienced Stratosticians But we can still get split events from wave one events I think the Christmas warming in 2018 was a wave one?  thanks in advance

 

It's Wave 2 normally that causes splits and Wave 1 for displacements. Extract from 2012 research below. Lots of similar studies in the Research Library under various stratosphere headings.

Identification and Classification of Stratospheric Sudden Warming Events
Section 1.3.1. Displacement vs. Split
During a SSW the wintertime polar vortex temporarily disappears around the same time the mean zonal wind reverses from westerly to easterly. Before the vortex completely disappears it is deformed into some irregular shape as it begins to dissipate. During this deformation the vortex is generally considered to deform into one of two distinctly different ways. The first is when the vortex drifts away from the pole toward lower latitudes. This is known as a “displacement” type event, and it is characterized by the fact that the vortex deforms into a “comma” shape as it is weakening. The other type of event is when the vortex is split into two smaller vortexes and each of these drifts separately away from the pole before dissipating, such events are known as “split” type events. Each of these developments have distinctly different effects on lower atmospheric dynamics. Specifically, during a split event deformation of the vortex is distinctly barotropic, while during displacement events the vortex tilts west-ward with altitude (Waugh and Polvani, 2010). It is not entirely clear what causes these two different scenarios. Often a correlation is made between the type of Rossby waves that caused the SSW and the type of event: if the waves which cause the event are mostly of wave number 1 it is a displacements, and if they are wave number 2 it is a split. However, there also seems to be some relationship to the preconditioning of the vortex before the event based on atmospheric blocking in lower layer of the atmosphere (Martius et al., 2009; Taguchi, 2008).

Source: https://commons.erau.edu/cgi/viewcontent.cgi?referer=https://www.google.co.uk/&httpsredir=1&article=1061&context=edt

[Catacol]

3 hours ago, Mike Poole said:

I guess there is concern that the strat vortex is bound to imprint on the trop vortex at some point and the result will be weeks of mild wet and windy weather for the UK.  But what if the opposite happened?

Plot shows the Northern Annular Mode timeseries at all levels of the atmosphere, the end of the forecast period is intriguing (from GFS 0z run).

Hmmmm interesting. Only another representation of NWP data which we know lacks reliability BUT there is a sniff here of the long term impact that a recurrent Sceuro high and North Pacific low may have begun to have with the +EAMT adding further stress and bottom up forcing. 10hpa zonal wind forecasts for the season are seeing a growing number of members agreeing on below average speeds into January. Signs that this winter may not be the zonal wash out feared are perhaps on the up, for the moment at least.

[Catacol]

Here we go - following the moderate but relatively sustained wave 2 squeezing the beginning of something a bit more significant from a wave 1 angle as we approach mid month. Intrigue grows. 

[Paul_1978]

 

[DavidS]

7 hours ago, Paul_1978 said:

 

Yep, certainly looks that way. 
Both uncorrected an bias corrected CFS showing significant weakening of zonal winds.

 

[Paul_1978]

2 hours ago, DavidS said:

Yep, certainly looks that way. 
Both uncorrected an bias corrected CFS showing significant weakening of zonal winds.

 

Surely the main impact of this is less likelihood of an Atlantic onslaught over the coming weeks.