Stratosphere and Polar Vortex Watch 2020

[MATTWOLVES 3]

41 minutes ago, Griff said:

 

@MattHugo has just tweeted too.

Matt please come back, talk to us! 

I'm here mate,don't stress.. joking aside some good signs this evening from the 46..and some better signs on a possible split.I think I've heard someone pointing out the MJO moving into phase 6 which spells bad news for the Eastern States moving forward..personally folks I think we are in a better position..

Edited January 18, 2021 by MATTWOLVES

[stodge]

The possibility of heights developing over Scandinavia has been on the cards for a few days.

As I see it, IF we get the PV back over to the Canadian side, assuming it is still weak from all the warmings and SSW displacements, it won't be enough to prevent Scandinavian height rises and from ther eit can get very interesting.

My personal view would be the UK being the battleground between cold and mild airmasses in early February with the cold winning out through the middle of the month.

[Don]

57 minutes ago, stodge said:

The possibility of heights developing over Scandinavia has been on the cards for a few days.

As I see it, IF we get the PV back over to the Canadian side, assuming it is still weak from all the warmings and SSW displacements, it won't be enough to prevent Scandinavian height rises and from ther eit can get very interesting.

My personal view would be the UK being the battleground between cold and mild airmasses in early February with the cold winning out through the middle of the month.

Hopefully the ongoing attacks on the PV will help overcome La Nina's milder signal for the second half of winter?  I saw on Gavin Partridge's video yesterday that it is shifting to more centre based which is conducive to milder patterns later in winter.  However, at the same time the North Eastern Pacific region is cooling after being in a warm phase for some time and this could help suppress the jet stream which again would help aid blocking.

[DavidS]

GFS 0z having a good go at split in FI

[DavidS]

GEFS also looking to keep zonal winds weak or reversed

[Vikos]

Looking good for a Split upstairs. But still needs to reach troposphere. Downwelling will take some time, no signals on a PVS in troposphere, yet

10hPa

 

 

30hPa

 

in 50hPa winds slow down, but no negatives, but patterns seem to follow upper levels.

 

In 150hPa (Strat-2-Tropo layer) still looking quite zonal, winds remain all positive

 

Regarding those zonal winds, well....

 

From    to---->

 

Wait and see. Honestly, atm I see a patt situation, outcome unknown. GFS looks good, though.

 

[Interitus]

On 17/01/2021 at 17:54, Frostbite1980 said:

No disrespect to Marco but he has been saying about the SSW possibly causing cold air into the uk etc when it first started and it didnt work out like that so i will take this tweet as a pinch of salt....no idea comes to mind 

Maybe not quite no idea, but little idea with regards to details - and this probably goes for all tweets and analyses by whomever.

 

17 hours ago, Bricriu said:

Not me. I got stuck at WAF. Wave forcing??

Wave Activity Flux - which is essentially wave forcing, propagating up through the atmosphere.

[Interitus]

On 16/01/2021 at 07:40, sebastiaan1973 said:

Why is it ironic? I try to understand/ learn

Sorry for late reply. You posted charts which take their inspiration from these classic images -

Tim Dunkerton was one of the authors of these, but sadly didn't respond to the Cohen tweet with anything as insightful regarding the current situation going forward.

[sebastiaan1973]

41 minutes ago, Interitus said:

Sorry for late reply. You posted charts which take their inspiration from these classic images -

Tim Dunkerton was one of the authors of these, but sadly didn't respond to the Cohen tweet with anything as insightful regarding the current situation going forward.

Okay. I know Tim Dunkerton (2001) was one of the first. But I didn't understand what is ironical about this. Now, I know. Thanks.

 

Far away... so uncertain, we see a the main vortex displaced to Canada. In my opinion this creates some space for a Scandinavian Anticyclone.

 

[Monotone]

Scandinavian blockade scenarios began to emerge in the first week of February. This is a tragic development during this period when the Siberian thermal springs began to move. For example, there was no such action until 10 days ago. The scenarios that led to the Greenland blockade were dominant. And now there are outputs that give this scenario. While the dominant scenario is the Scandinavian blockade (in this scenario there is a possibility that Siberian thermals will land in Eastern Europe), if the Greenland congestion occurs, the Siberian Thermal will go to Western Europe and it will be very cold. The first week of February is very complicated. We have to wait .. The beginning of February actually determines the fate of February. If there is a blockade of Greenland instead of the Scandinavian, the system will not descend into Eastern Europe until the 15th, but from the 15th it can receive systems suspended in Central Europe. The Middle East is entering a dry and arid period. I used my guess for the Greenland blockade in early January. Because there was no scenario for the Scandinavian blockade. But now there is the possibility of a Scandinavian blockade and I am hopeful. If the stratospheric displacement phenomenon provides mating, we will see many more actionable images. I think EPS suggested such a scenario based on this possibility. Stratosphere warming may occur at the end of February. It is not yet clear whether it will be FSW or SSW. Images: ECMWF expects February with a focus on West-Central Europe.

 

 

 

 

Edited January 19, 2021 by Monotone

[Bricriu]

I can't see a scandi' high lasting if the vortex over Canada has some oomph to it. You would imagine in that scenario  low pressures will be dominating our weather

[Vikos]

For me, this looks good

 

 

[Frostbite1980]

1 hour ago, Vikos said:

For me, this looks good

 

 

Whys that then? 

[chionomaniac]

On 18/01/2021 at 21:06, Griff said:

Anyone competent to have a shot at dissecting and evaluating this? 

Thanks. 

@chionomaniac

I’ve seen a bit of chatter about a possible vortex split towards the end of the runs. But these lack the consistency and have not drawn in at all. To me, compared to the wave 1 event, which was consistent and did draw in, I think that there is no reliability in these forecasts and very unlikely to happen. We need to see a split run after run and being drawn in, so I have very little confidence that this will occur until these conditions are met.

[Snowman.]

3 hours ago, Bricriu said:

I can't see a scandi' high lasting if the vortex over Canada has some oomph to it. You would imagine in that scenario  low pressures will be dominating our weather

They can exist along side the Scandi ridge, allowing for good undercut and frontal snowfall potential too. Tbh with Scandi heights I always like to have something to the NW so the high doesn't drift away too far.

 

Edited January 19, 2021 by Snowman.

[sebastiaan1973]

[Vikos]

 

Temperatures in the NH are dropping fast, that is an outcome of those stratospheric disturbances taking their influences.

[Interitus]

2 hours ago, Vikos said:

 

Temperatures in the NH are dropping fast, that is an outcome of those stratospheric disturbances taking their influences.

Looks more like temperatures in the forecast period reverting to climatology.

[Vikos]

24 minutes ago, Interitus said:

Looks more like temperatures in the forecast period reverting to climatology.

Even then it's still a strong down development

[Flake news]

On 20/01/2021 at 15:42, sebastiaan1973 said:

It bewilders me the effort some people put into twitter posts, these days i struggle to complete a senten

[Griff]

Latest ecm zonal... 

[JeffC]

Interesting stuff at 10 hPa

 

Edited January 21, 2021 by JeffC
Forgot the pic

[sebastiaan1973]

Summary: Historical analogs point to the likely impacts of a weak stratospheric polar vortex and an amplified MJO forecast

In a dramatic break with the pattern of recent years, this winter has seen strong and persistent high-latitude blocking that has produced unusual cold across most of Russia and East Asia. The Arctic Oscillation has been significantly negative since early December, and the North Atlantic Oscillation will be negative for both December and January for the first time in a decade. The figure above shows the AO index from the past few months; this figure – and all others in this post – are available to World Climate Service customers in our online portal.

Sudden Stratospheric Warming

While the initial onset of a negative AO pattern in December occurred in conjunction with a relatively strong polar vortex in the stratosphere, a sudden weakening of the vortex around the turn of the year created a much more coherent Arctic anomaly, with strong vertical coupling between the troposphere and the stratosphere. The 10mb westerly flow at 60°N reversed to an easterly direction on January 5, marking the occurrence of a “sudden stratospheric warming” event.

This diagram shows the time evolution of the vertical profile of geopotential height anomalies for the past 30 days and in the 15-day ECMWF forecast. Above-normal heights from 10-200 hPa indicate the weaker-than-normal condition of the stratospheric polar vortex since late December. Above-normal heights from 500-1000 hPa are associated with a negative AO phase.

Remarkably, the stratosphere polar vortex has shown little recovery in the more than 2 weeks since the vortex disruption, and recent forecasts are showing another round of weakening – after a brief recovery – in the next two weeks.

MJO Forecast

The expected re-weakening of the stratospheric westerlies is linked to another major anomaly that models are expecting to emerge by early February: a very strong pulse of MJO wave energy in the western Pacific. The MJO index is predicted to move into phases 6 and 7, which are favorable for additional weakening of the polar vortex; this is because the transfer of wave energy from MJO 6/7 into the North Pacific lines up with the climatological stationary wave and enhances the upward energy flux that disrupts the westerly flow aloft. The relatively predictable evolution and well-known global impacts of the MJO provide a foundation for long-lead forecasts worldwide.

As an aside, the GEFS extended ensemble forecast has been calling for an MJO transition into phases 6 and 7 for several weeks, and while the GEFS was a bit too early with this, its long-lead MJO forecast provided a major hint that disruption to the polar vortex could be long-lived. Here’s our MJO forecast graphic from December 29.

Analog Analysis of Impacts

What can we say about potential impacts from this remarkable alignment of a strong MJO 6/7 pulse and an already-weak stratospheric vortex? To answer this, we glean insight from the World Climate Service subseasonal index analogs tool, which allows users to explore combinations of different climate phenomena.

Using the WCS tool, we first search for historical dates with both a strong MJO phase 7 and a weak vortex at 10mb within two weeks either side of February 10; according to the GEFS forecast, both criteria will be satisfied on this date. A set of 11 matching historical dates are as follows: 1978/02/04, 1981/02/20, 1987/02/09, 2001/02/25, 2002/02/23, 2006/01/30, 2010/01/28, 2012/02/06, 2013/01/26, 2017/02/09, 2018/02/14.

Next, we examine the temperature patterns that occurred in the weeks surrounding these analog dates. For example, 8-14 days prior to the matching dates, most of eastern North America was often warmer than normal, while Europe tended to see cold in the north and mild conditions in the south. This bears some resemblance to the current week 2 model forecasts – compare the two maps below – and suggests that the analogs do have some relevance to the current situation.

If we then step ahead week by week, the analogs reveal the typical sequence of events when the MJO/PV criteria were met at this time of year in the past. In the 7 days leading up to the matching dates, Europe tended to see a much stronger cold signal develop, with a focus on western and central areas; but warmth was dominant in the southern and eastern U.S.

Interestingly, week 3 in the current subseasonal models again shows some similarity to the analog signal, with cold expanding across Europe relative to the previous week, but with a warm signal remaining in the eastern U.S.

Looking beyond the February 10 matching date, the maps below show the typical outcome for 4 more weeks, which would take us all the way to early March. Cold persists in Europe, with the signal only gradually weakening and retreating to Scandinavia, and a strong warm signal develops over Canada in the second week. Perhaps surprisingly, there is no compelling sign of cold in the eastern U.S. until week 4, i.e. early March, although the analogs see cold developing in the western U.S. in weeks 2 and 3, i.e. late February.

The cold signal in Europe is closely associated with a blocking ridge near Greenland and Iceland, and a southward-displaced jet stream in the North Atlantic. Again the pattern compares very favorably between the analog analysis and the current model forecasts for weeks 4-5.

In summary, historical analogs suggest that the combination of a strong MJO wave in phase 7 with a weak stratospheric polar vortex is rather likely to bring widespread cold to Europe in early-mid February. This outlook is broadly similar to the dynamical model forecasts, but the analogs suggest a greater cold risk in western Europe than the models are currently indicating. In contrast, neither the analogs nor the models show any sustained or significant cold in the eastern U.S. until early March.

Finally – and just to illustrate further the utility of the WCS analog tool – it’s worth showing that it’s the combination of a weak polar vortex with MJO phase 7 that produces the strong cold signal for Europe. For instance, past occasions with strong MJO phase 7 and a strong polar vortex have warmth in eastern and northern Europe, and nearly the opposite temperature pattern in North America.

Alternatively, if we remove the MJO criterion and only look at dates with a significantly weakened polar vortex, there’s a modest cold signal over western Europe, but it’s much less compelling than when a phase 7 MJO develops at the same time.

-> the whole story with pictures ->

MJO Forecast and Stratospheric Warming: Impact of Extremes - World Climate Service

WORLDCLIMATESERVICE.COM

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Summary: Historical analogs point to the likely impacts of a weak stratospheric polar vortex and an amplified MJO forecast

 

[Mike Poole]

I think the latest NAM plot from Stratobserve is interesting, and reflects the way things seem to be panning out.  You can see the downwelling initially quite well but then it hits a hump while the trop was not willing to properly engage, and then hopefully, by this run anyway, that hiatus is now behind us, maybe aided my MJO:

[sebastiaan1973]

Influence of stratospheric sudden warming on the tropical intraseasonal convection - IOPscience

IOPSCIENCE.IOP.ORG

Abstract

Madden–Julian oscillation (MJO), the dominant mode of intraseasonal variability in the tropical troposphere, has recently been shown to have a great impact on Northern Hemisphere (NH) extratropical stratosphere. But the influence of the variability in the extratropical stratosphere on MJO is seldom reported. In this study, the influence of major, mid–winter NH stratospheric sudden warmings (SSWs) on the MJO is investigated using meteorological reanalysis datasets. Our analysis reveals that SSWs also exert considerable influence on tropical intraseasonal convection. The occurrences of MJO phases 6 and 7 significantly increase during around 20 d after the onset of SSWs, corresponding to enhanced convective activity over the equatorial Central and Western Pacific. Then in the following days, the coherent eastward propagation of tropical intraseasonal convection resembles the periodic variation in a typical MJO. These results suggest that the extratropical stratosphere affects the organized tropical intraseasonal convection, and variability of the tropical intraseasonal convection related to MJO can be better grasped by taking extratropical stratospheric variability into account. Considering the complex interaction between MJO and extratropical stratosphere, further work on comprehensive understanding of the relationship between SSWs and MJO is required in future studies.