Stratosphere and Polar Vortex Watch 2020

[phil nw.]

59 minutes ago, sebastiaan1973 said:

He mentions the normal response time, as mention in literature.  I think it can matter what your definition is of impact. Is it e.g. NAO? Or something else

The ideal impact for cold and snow lovers would be a neg AO/NAO with the jet kicked just south of the UK. Greenland to Scandi. blocking.

 

 

 

 

 

[WINTRY WALES]

34 minutes ago, phil nw. said:

Yes as I understand from reading stuff the downwelling effect on the trop pv can take anything between 2 to 6 weeks. 

Let's hope with an already weakened tpv this Winter we see a quick response. 

 

Surely this a crumb of comfort for coldies at present. With the official SSW only confirmed today and amount of downwelling etc yet to be concluded there must be a fair amount of “Volatile” data currently feeding the models. How can we not expect the current  model output to be anything but “volatile” or indeed “inaccurate” in the very early stages of the SSW that we are in??

Edited January 5, 2021 by WINTRY WALES

[Anthony Burden]

1 hour ago, Weather-history said:

I'm confused here. 

Alex Deakin mentioned in the Met Office 10 day trend broadcast last Wednesday about a possible SSW which could have an impact " but in a number of weeks time"

That says to me, the Met Office  don't expect see any possible impact until late January into February at the earliest

So why are some people thinking that we should be seeing the models reacting to this almost straight away?

Not really e-mail from Marco Patanga stating mid month to end month possible.

[SqueakheartLW]

Wonder if this is the first signs on the model output of the tropospheric response

[Blessed Weather]

2 hours ago, sebastiaan1973 said:

Please notice this is at 60N! For the area of the first impact you have in my opinion look further to the north. So for honesty and reflection. The charts I posted first, were for 60N. And now I learn this is quite common for a SSW.

Is it me? Whilst I have enormous respect for Simon Lee I found the above tweet was somewhat muddled (but I do realise that Twitter character limitations make clarity difficult). If he is saying mean zonal winds below 30hPa and 60N rarely (if at all) go easterly as a mean flow around the entire circumference of the globe, then fair enough. But following a SSW easterly zonal winds certainly do descend below 30hPa all the way down to the surface as today's Berlin ECM charts for 4th and 13th January show:

4th:  13th:

And the chart marked by Chiomaniac in his post of 2nd January shows that easterly zonal winds at the surface can certainly be expected at 60N:

 So was the real point Simon was trying to make that zonal wind anomalies are better for monitoring SSW downwelling to the surface? Any other views or am I going off on one. 

Edited January 5, 2021 by Blessed Weather
Tweek to clarify a sentence.

[phil nw.]

Yes that's a bit confusing.Surely negative anomalous zonal winds downwelling is another way of saying a reduction is downwelling.

It's clear to me that for the NH trop.pattern to reverse or retrogress then easterly zonal winds have to reach the surface as shown in the image.

[phil nw.]

1 hour ago, WINTRY WALES said:

Surely this a crumb of comfort for coldies at present. With the official SSW only confirmed today and amount of downwelling etc yet to be concluded there must be a fair amount of “Volatile” data currently feeding the models. How can we not expect the current  model output to be anything but “volatile” or indeed “inaccurate” in the very early stages of the SSW that we are in??

The main thing is the lag effect on the 500 hPa modeling.There will likely be a bit of a wait until NWP fully absorb the down welling.

I am thinking from a quick response perhaps another week or so before it comes into view on the later frames,longer  if the filtering down of the warming is slower.It's a bit of a guess as each event is a bit different.

Edited January 5, 2021 by phil nw.

[Bricriu]

So if downwelling reaches the troposphere, then stops, only to uptick again, will this be enough to facilitate height rises in the places we'd all like to see them?

[phil nw.]

2 minutes ago, Bricriu said:

So if downwelling reaches the troposphere, then stops, only to uptick again, will this be enough to facilitate height rises in the places we'd all like to see them?

That's the 64.000 dollar question.

If we get the response we hope for we will see Blocking heights across some parts of the Arctic.I don't think anyone could say where they will set up at the 500 hPa level exactly,not until near time NWP get's a handle on the pattern.

We need some luck on that so that we end up on the cold side of any ridging/troughing-if your a coldie.

[sebastiaan1973]

1 hour ago, Blessed Weather said:

Is it me? Whilst I have enormous respect for Simon Lee I found the above tweet was somewhat muddled (but I do realise that Twitter character limitations make clarity difficult). If he is saying mean zonal winds below 30hPa and 60N rarely (if at all) go easterly as a mean flow around the entire circumference of the globe, then fair enough. But following a SSW easterly zonal winds certainly do descend below 30hPa all the way down to the surface as today's Berlin ECM charts for 4th and 13th January show:

4th:  13th:

And the chart marked by Chiomaniac in his post of 2nd January shows that easterly zonal winds at the surface can certainly be expected at 60N:

 So was the real point Simon was trying to make that zonal wind anomalies are better for monitoring SSW downwelling to the surface? Any other views or am I going off on one. 

Blessed Weather. Here's my guess. The charts Simon selected was just at 60 N. The pictures how show are the entire area from SH to NH. We see downwelling north of 60N. I guess that the chart made by chio pointing out the 60 N anomaly was not caused by downwelling, but has another reason.

[sebastiaan1973]

59 minutes ago, Bricriu said:

So if downwelling reaches the troposphere, then stops, only to uptick again, will this be enough to facilitate height rises in the places we'd all like to see them?

Yes, how much downwelling is needed.

[sebastiaan1973]

 

[Paul_1978]

2 hours ago, Blessed Weather said:

Is it me? Whilst I have enormous respect for Simon Lee I found the above tweet was somewhat muddled (but I do realise that Twitter character limitations make clarity difficult). If he is saying mean zonal winds below 30hPa and 60N rarely (if at all) go easterly as a mean flow around the entire circumference of the globe, then fair enough. But following a SSW easterly zonal winds certainly do descend below 30hPa all the way down to the surface as today's Berlin ECM charts for 4th and 13th January show:

4th:  13th:

And the chart marked by Chiomaniac in his post of 2nd January shows that easterly zonal winds at the surface can certainly be expected at 60N:

 So was the real point Simon was trying to make that zonal wind anomalies are better for monitoring SSW downwelling to the surface? Any other views or am I going off on one. 

The other thing with Twitter is that you can post a "thread" of Tweets. There are two others that Simon followed up with which I will paste below:

https://twitter.com/SimonLeeWx/status/1346420919103795200?s=20

https://twitter.com/SimonLeeWx/status/1346420923147186176?s=20

 

[bluearmy]

Berlin gonna be fun to look at tomorrow 

     

[Blessed Weather]

Thank you for clarifying Simon.

"Just to ensure this is clear - I'm not saying easterly winds associated with a major SSW don't reach the troposphere (they do, as can be seen in both the ECMWF cross-section & GFS forecast at 850 hPa). But 60°N itself doesn't often reverse, only weakens."

 

[SqueakheartLW]

Yet more signs of a 3rd warming in the 12z at the back end of the GFS runs

Parallel

26 of 32 GFS 12z runs show the 3rd warming, the highest number of the runs so far and so does the 12z parallel GFS run too. Not only is it the highest number so far the warmings on average are stronger and some are now before 384 hours away too. This is the strongest signal yet that the stratospheric story is far from resolved

[Blessed Weather]

Dr. Amy Butler clarifying that we do not have a split vortex as yet. Furthermore, the majority of multi-model ensemble members continuing to forecast a displaced vortex rather than a split out to 18th January. 

The vortex at 10 hPa is currently displaced over the North Atlantic... it has *not* split yet (except possibly in the very upper stratosphere), though there are indications it possibly could in another week (only 8/74 forecast members suggest that to be the case though).

Source: Twitter @DrAHButler

Which leads me to refer to last evening's (4th Jan) blog by Judah Cohen that:

......"some early research tried to argue that there are tangible differences between PV displacements and splits, more recent research has shown there are little substantive differences in the weather. Instead, the ensuing weather flowing both PV splits and displacements are nearly indistinguishable."

I've yet to locate the "recent research" that Judah refers to. Does anyone know of such research and able to give me a link please. Thks.

Edited January 5, 2021 by Blessed Weather
Clarification of ensemble forecast.

[damianslaw]

8 hours ago, phil nw. said:

Yes as I understand from reading stuff the downwelling effect on the trop pv can take anything between 2 to 6 weeks. 

Let's hope with an already weakened tpv this Winter we see a quick response. 

 

There are examples of very quick effects, early Feb 2009 a good example. I think on average you should expect at least 2 weeks, Feb 2020 was about 3 weeks later, so based on this late Jan is probably when we should feel the full effects.

[Don]

26 minutes ago, damianslaw said:

There are examples of very quick effects, early Feb 2009 a good example. I think on average you should expect at least 2 weeks, Feb 2020 was about 3 weeks later, so based on this late Jan is probably when we should feel the full effects.

Do you mean February 2018?

[Vikos]

48 minutes ago, Blessed Weather said:

I've yet to locate the "recent research" that Judah refers to. Does anyone know of such research and able to give me a link please. Thks.

Maybe here

AO Blog Update | AER | Weather Risk Assessment

WWW.AER.COM

---

January 04, 2021 - Dr. Judah Cohen from Atmospheric and Environmental Research (AER) embarked on an experimental process of regular research, review, and analysis of...

 

[ALL ABOARD]

If at first you don't succeed 

 

Try 

 

Try 

 

Try again? 

 

[damianslaw]

37 minutes ago, Don said:

Do you mean February 2018?

Oh yes mistake

[Weather-history]

Maybe we should look at the list of SSW/MMW/Canadian events and then compare what happened after these events on the UK weather, we've got a CET list to work with?

Matt Hugo just metioned this in  a tweet and something I have mentioned as well, if you aready in a blocked postion, do you want a SSW event that could disrupt the block? 

[Blessed Weather]

9 hours ago, Vikos said:

Maybe here

(Snipped)

Thanks. Cohen refers to the research in that blog but as far as I could see doesn't provide a link to it.

In the meantime, with the current SSW looking increasingly like a displacement event, some relevant snippets from the 2016 research paper Stratospheric polar vortex splits and displacements in the high‐top CMIP5 climate models. Of particular interest regarding when NWP output might start reflecting the SSW impact, the last bullet point below that displacements often take weeks to propagate down versus the much quicker impact from a split:

• Vortex splits show a slightly stronger North Atlantic surface signal in the month following onset. However, the most significant difference in the surface response is that vortex displacements show stronger negative pressure anomalies over Siberia.
• We have also found that there are some consistent differences in surface anomalies following the two types of event. In particular, MSLP anomalies following displaced vortex events are more negative over Scandinavia and Siberia than following split vortex events.
• ......[displacements are more baroclinic so that] anomalies associated with vortex displacements descend through the stratosphere over a period of weeks. .......[whereas vortex splits occur barotropically which] results in a stronger instantaneous annular mode‐like signal at the onset of vortex splits.

Source: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JD024178

 

Edited January 6, 2021 by Blessed Weather
Contents of quote box snipped to shorten post.

[bluearmy]

56 minutes ago, Weather-history said:

Maybe we should look at the list of SSW/MMW/Canadian events and then compare what happened after these events on the UK weather, we've got a CET list to work with?

Matt Hugo just metioned this in  a tweet and something I have mentioned as well, if you aready in a blocked postion, do you want a SSW event that could disrupt the block? 

Ed mused this back in December ...... I guess the reply is that with no ssw we could have possibly maintained a decent trop scenario for another couple weeks but later in jan and into feb would likely have gone to mobile. We could now see latter third jan and through feb with downwelling waves ..