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Model output discussion - proper cold spell inbound?

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Nobody is really expecting another 47 or 63 Quicksilver but as a climatologist you will also know that we don't need that to have a notably cold and/or snowy spell. My own fave of feb 1978 didn't make it into the top 20 winters of the twentieth century yet I still got12-18 inches of snow on the south coast of England. 

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33 minutes ago, Quicksilver1989 said:

Well lets see what the science says about it all shall we?

There is considerable evidence that SSW's have an impact on atmospheric circulation patterns, indeed many studies have confirmed this. It provides a significant increase in forecasting skill.

But first what in an SSW event?

This refers to a warming of upto 50C in an area of the atmosphere 10-50km above the earth's surface. High up in the atmosphere we have the polar night jet, which can bend if we get blocking features in the lower atmosphere. If enough pressure is placed, the jet can break. In these scenarios air in the stratosphere collapses leading to a warming in our stratosphere. The easterly winds begin sinking from the stratosphere into the atmosphere and we start seeing the changes in atmospheric circulation, but this can either take place over days or weeks.

A recent paper by the Met Office (Scaife et al 2015) sheds some light on the impacts, here is a key figure:

image.thumb.png.a4d72ca35792e95c1bea823b3d82f5eb.png

What is this showing? Well its comparing the forecasting model of the winter NAO with and without taking SSW's into consideration. We can see that factoring in the probability of an SSW increases the forecasting skill of the model dramatically. This underlines how useful understanding our stratosphere can be.

How likely will that translate into surface cold here in the UK? and how negative did the NAO actually go? Here I look at 2 key events:

1) The most obvious example of an SSW directly impacting the UK is the 24th January 2009 event. Some similarity to what we are seeing now.

26th January 2009                                       Early February 2009
NOAA_1_2009012618_1.pngNOAA_1_2009020218_1.png

Quite an impressive transformation but outside of early February did it really do much? The rest of February was mild and the NAO was only neutral for that month.

5th January 2004                                        21 January 2004
NOAA_1_2004010518_1.pngNOAA_1_2004012118_1.png

This one was not really noteworthy in the UK or western Europe, its effects were far harsher over the eastern USA.

Out of the 22 SSW events since 1981- I'd say only 50% have led to UK cold spells at varying times after they occurred though. Hence my caution. You can see the impact it has on NH temperature anomalies in this figure by Deser et al (2014)

image.thumb.png.babd0a9232d7e621342ebeb0ab74b068.png

Of course its over 60 days but generally the main areas are more the eastern USA and Scandinavia extending out to Eurasia for more increased cold air outbreaks.

Finally we are getting to the time of year where easterlies do not always equate to cold. Look at the SSW event of February 1999 for example:

NOAA_1_1999031118_1.png

After a brief cold spell a few days earlier it actually turned very mild despite some fantastic northern blocking. So I think my post is a valid one. Increased chances of cold? definitely. Snowy cold spell? More likely but absolutely no guarantees. Prolonged cold? Again even more ambiguous. Not pessimistic, just realistic.

As for nothing has changed well... it has. Why do you think the 1740s to 1890s, 1940s to 1960s and 1980s saw far more cold spells then what we see now? Climate change. That is why. If we were in the 1800s, don't you think a lot more colder solutions would be verifying compared to what we see today? Here is an interesting paper from 2003, detecting anthropogenic influence on SLP. The clear trend to our south has remained.

image.thumb.png.f1aa8d259c1cf8049ec8ee4e2b7524a7.png  Trend in winter SLP

Why was 2010 so blocked then? Well that was to do with a slowdown in the overturning circulation that has been well documented. In general though I expect the trend in the above Figure to continue. Indeed the Atlantic cold blob has been a defining feature in recent years. Hopefully that will go away. However this is something predicted by the climate models and also in global surface temperature trends.

                           Grrr                                          Temperature trend from 1900-1912
image.thumb.png.a2e9c95f724c794f73389dc4046b24d0.png1900-2012-temp-trend-lrg.png

Sneachtastorm  - 1 hour ago

What upper nonsense


Any claims to back that statement up, I believe I am in some position to have a say given I am a PhD climatologist. What about you?

Overall, increased chance of a cold outbreak over the next 1-4 weeks, especially from the east but don't be so certain of a snowy solution or a notably cold one for our area...

 

I don’t think you can use a ‘normal’ SSW as a benchmark. So I’m told this one has some uniqueness. 

Dr Cohen likes to 1985/1991 as anologues of upcoming split of which both winters delivered some spectacular winter weather the latter much less prolonged and perhaps more arguable in resultant conditions considering cold peaked relatively early in the month perhaps the efffects of SSW were instantaneous. I don’t think anyone should be certain. However, it’s clear to see, we stand a much greater chance GFS has consecutively being putting out very good FI charts. And the last day it’s picking up in semi reliable timeframe as below easterly in 10 days time.

GFS 00z gives an easterly within the next 10 days technically, and it turns into a snowy one too. No doubt MJO imo is why we’re seeing interest in a Scandi high but the SSW will decrease perhaps substantially the zonal westerlies across the Atlantic which are often the nail in the coffin, meaning we stand an increased chance of a prolonged easterly cold spell. I’m absoloutely no expert but even I see considerable potential. 

E8554BF1-581C-4401-B154-8F95664BC18D.thumb.png.24f5255b06f48d7faef110dbb4f4a142.png4E9B883C-6D16-48F2-8AFE-91C7603016B2.thumb.png.fded4fcb56554435fd97cda08b4a137e.png

From his latest blog..

Impacts

The predicted stratospheric PV split and the tropospheric response is likely to dominate the weather across the Northern Hemisphere through the end of winter. Most model runs predict that the PV disruption will qualify as a major mid-winter warming (where the winds reverse from westerly to easterly at 60°N and at 10hPa) though I don't consider it critical for the forecast. The PV disruption is unusual in that it is predicted to result in one primary stratospheric PV over North America. I also find it unusual that both sister vortices advect/transport significant amount of heat towards the equator simultaneously even after the split. Thanks to Twitter peeps Jonathan Wall (@_jwall), Swaginator457 (@BruenSryan) and Zac Lawrence (@zd1awrence) for their help identifying the best analogs for the predicted polar vortex split. I would say that the best analog was early January 1985 (central date of January 2) followed by early February 1991. Two weeks following the January 1985 PV split one of the greatest historical Arctic outbreaks was unleashed into the Eastern US (January1985cold). This contrasts with February 1991 that was an overall mild month though the end of the month was slightly below normal temperatures across the Eastern US with more significant cold in Eastern Canada. The temperature response across northern Eurasia was more consistent including Europe. For both January 1985 and February 1991 cold was widespread across much of Europe.

https://t.co/LahzvNZ6yj

There’s so much potential :D

 

Edited by Daniel*

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45 minutes ago, Quicksilver1989 said:

Well lets see what the science says about it all shall we?

(Edited for brevity - sorry Q)
 

Really interesting post this Quick. I think most of us are hopeful of winter's last gasp being an icy cold one thanks to the SSW but as you rightfully point out, nature is often keen to blow a mild Southwesterly-based raspberry in our faces whenever we least expect it. What I do like about this particular stratospheric event is the extent to which the models are predicting favourable blocking and thereafter an Easterly flow from such a long way out (vis a vis METO update). How the next ten days or so unfold is going to make for fascinating model watching that's for sure - let's hope we can find our salvation from the right direction for once and not be forced to witness a dramatic climbdown day by day as we've suffered so many times in recent winters. Been through the GFS ensembles this morning - some unbelievable eye candy in there, by no means all of it at 384 hrs for a change. This my particular favourite (Pert 4) but there are lots more of equal interest.

tempresult_tdd7.giftempresult_ely2.giftempresult_tar3.gif

 

PS. Probably better if last few sentences of your post had been a bit less adversarial but that doesn't mean the rest of it wasn't fascinating :) 

Edited by supernova

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Back to the models, the GEFS ensembles have trended significantly colder over night after day 9/10 with the mean down below -5 which is very unusual given how far out it is, wintery weather is not guaranteed BUT given the SSW and background signals, a cold spell is much more likely than normal with the current vortex position.

Edited by Weathizard

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1 minute ago, Quicksilver1989 said:

Well it was actually very relevant to the post I was making so no I won't post it in a different thread. You're not a mod. If you don't like it then that's your decision but its still a valid point to make in the model output discussion thread.

I think that is a fair enough comment from my viewing of the discussion over the past couple of pages. Interesting the differences and by the end of February we may know the answer. Beyond me but interesting to read the posts.

In terms of my ability then the anomaly charts continue to predict quite marked northern blocking. As yet, to me, it does seem too far north to have any marked effect although I am perhaps not interpreting what they show correctly. One could postulate that any surface lows are likely to track rather further south than they normally do. Behind any one of these deep lows then a northerly could develop and this might bring the blocking further south, at least on a temporary basis. Once there then deep cold might be hard to shift?

Just an idea.

Anyway below are the usual links. The 8-14 NOAA if you click on it keeps the northern blocking. One final comment, alluded to above, is that these are mean charts.

http://www.cpc.noaa.gov/products/predictions/610day/500mb.php

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

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2 hours ago, chionomaniac said:

Great trend, finally, from the later stages of the ECM. Most satisfying seeing a kind of pattern that I have been anticipating and suggesting finally turn up. (that's relief not big headedness btw! lol) Now we just need to get any cold to filter our way.

I did find it odd though how the blocking to our N/NE is held at bay for so long by a weak trough extension NE from the UK. Related to the trough being so deep and the jet wrapping around a bit, but past experience suggests the jet can easily fire right on into Europe instead with the trough disrupting and secondary lows taking shape then sliding SE, so I am sceptical of the way the run evolves in the Atlantic sector. UKMO is a bit closer to achieving the disrupt-slide outcome so it will be of some interest to see (even in the limited view that we have to make do with) what the day 7 chart looks like when it comes along.

Elsewhere though, the trends with ECM and UKMO are indeed very promising and in line with what has been much advertised by expert minds :good:.

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12 minutes ago, Daniel* said:

I don’t think you can use a ‘normal’ SSW as a benchmark. So I’m told this one has some uniqueness. 

Dr Cohen likes to 1985/1991 as anologues of upcoming split of which both winters delivered some spectacular winter weather the latter much less prolonged and perhaps more arguable in resultant conditions considering cold peaked relatively early in the month perhaps the efffects of SSW were instantaneous. I don’t think anyone should be certain. However, it’s clear to see, we stand a much greater chance GFS has consecutively being putting out very good FI charts. And the last day it’s picking up in semi reliable timeframe as below easterly in 10 days time.

GFS 00z gives an easterly within the next 10 days technically, and it turns into a snowy one too. No doubt MJO imo is why we’re seeing interest in a Scandi high but the SSW will decrease perhaps substantially the zonal westerlies across the Atlantic which are often the nail in the coffin, meaning we stand an increased chance of a prolonged easterly cold spell. I’m absoloutely no expert but even I see considerable potential. 

E8554BF1-581C-4401-B154-8F95664BC18D.thumb.png.24f5255b06f48d7faef110dbb4f4a142.png4E9B883C-6D16-48F2-8AFE-91C7603016B2.thumb.png.fded4fcb56554435fd97cda08b4a137e.png

From his latest blog..

Impacts

The predicted stratospheric PV split and the tropospheric response is likely to dominate the weather across the Northern Hemisphere through the end of winter. Most model runs predict that the PV disruption will qualify as a major mid-winter warming (where the winds reverse from westerly to easterly at 60°N and at 10hPa) though I don't consider it critical for the forecast. The PV disruption is unusual in that it is predicted to result in one primary stratospheric PV over North America. I also find it unusual that both sister vortices advect/transport significant amount of heat towards the equator simultaneously even after the split. Thanks to Twitter peeps Jonathan Wall (@_jwall), Swaginator457 (@BruenSryan) and Zac Lawrence (@zd1awrence) for their help identifying the best analogs for the predicted polar vortex split. I would say that the best analog was early January 1985 (central date of January 2) followed by early February 1991. Two weeks following the January 1985 PV split one of the greatest historical Arctic outbreaks was unleashed into the Eastern US (January1985cold). This contrasts with February 1991 that was an overall mild month though the end of the month was slightly below normal temperatures across the Eastern US with more significant cold in Eastern Canada. The temperature response across northern Eurasia was more consistent including Europe. For both January 1985 and February 1991 cold was widespread across much of Europe.

https://t.co/LahzvNZ6yj

There’s so much potential :D

 

Yup there is the factor of where abouts the SSW occurs, this one is focused on Greenland so I expect the Arctic Oscillation at least to really dip. Our chances of a really good cold spell depend on whether the NAO plays ball and SLP to our south dips too. Generally in late February - May blocking patterns become more common, hence these often being amongst the driest months in the British Isles.

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50 minutes ago, Quicksilver1989 said:

Well lets see what the science says about it all shall we?

There is considerable evidence that SSW's have an impact on atmospheric circulation patterns, indeed many studies have confirmed this. It provides a significant increase in forecasting skill.

But first what in an SSW event?

This refers to a warming of upto 50C in an area of the atmosphere 10-50km above the earth's surface. High up in the atmosphere we have the polar night jet, which can bend if we get blocking features in the lower atmosphere. If enough pressure is placed, the jet can break. In these scenarios air in the stratosphere collapses leading to a warming in our stratosphere. The easterly winds begin sinking from the stratosphere into the atmosphere and we start seeing the changes in atmospheric circulation, but this can either take place over days or weeks.

A recent paper by the Met Office (Scaife et al 2015) sheds some light on the impacts, here is a key figure:

 

Really great post that. Very balanced overview.

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9 minutes ago, johnholmes said:

I think that is a fair enough comment from my viewing of the discussion over the past couple of pages. Interesting the differences and by the end of February we may know the answer. Beyond me but interesting to read the posts.

In terms of my ability then the anomaly charts continue to predict quite marked northern blocking. As yet, to me, it does seem too far north to have any marked effect although I am perhaps not interpreting what they show correctly. One could postulate that any surface lows are likely to track rather further south than they normally do. Behind any one of these deep lows then a northerly could develop and this might bring the blocking further south, at least on a temporary basis. Once there then deep cold might be hard to shift?

Just an idea.

Anyway below are the usual links. The 8-14 NOAA if you click on it keeps the northern blocking. One final comment, alluded to above, is that these are mean charts.

http://www.cpc.noaa.gov/products/predictions/610day/500mb.php

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

To me this is exactly where the ECM ensembles are right now.

By D10 on this morning's suite, you can see northern heights starting to build but far less than 50% have a direct influence on the UK at this stage.

By D13, cold but not deep cold is becoming the theme with the vast majority of runs seeing uppers between -4C and -8C widely (not to be dismissed on an easterly of course), but only about 5% of runs go colder than that.

The cold trend then actually eases slightly by D15.

Snow seems to have affected much of the UK at some point between D10/D15 but seems more focused towards the N and W, so probably from Atlantic incursions against cold air.

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11 minutes ago, Chris.R said:

If it ends up like February 2009 again then you can shove your SSW! A few flakes blowing in the wind, no thank you. 

We had 3 snowfalls of 4 inches in that spell. Each to their own. 

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2 minutes ago, karyo said:

Every GFS run seems to upgrade Sunday and Monday's cold uppers! Plenty of snow showers in a northwesterly wind, veering more westerly by Monday.

Exactly  i dont tend to take the GFS charts to literally however.  Wintry from Friday Morning  with the odd blip.  Favoured areas from that wind direction will see quite a bit of snow one would have thought.   Sunday also looks interesting.  The North West and places exposed perhaps by the chesire gap  should be quite happy with the output in the near term.   Interesting 

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6 minutes ago, weirpig said:

Exactly  i dont tend to take the GFS charts to literally however.  Wintry from Friday Morning  with the odd blip.  Favoured areas from that wind direction will see quite a bit of snow one would have thought.   Sunday also looks interesting.  The North West and places exposed perhaps by the chesire gap  should be quite happy with the output in the near term.   Interesting 

What i find particularly interesting is that Sunday's potential appears to be upgrading which is noteworthy for cold uppers coming from the west. Usually the opposite happens. 

Yes, tomorrow morning could surprise a few albeit it looks a bit more marginal than Sunday.

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And another potent West to North west flow next Thursday . -8 850s widely and a - 10 in Scotland. 

IMG_1299.PNG

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Morning all :)

A glorious winter's morning in lowland East London but one suspects the last of these for a while with a more changeable spell on the way.

This morning I'm looking at the journey in the model outputs to the early hours of February 19th:

Starting with ECM 00Z OP at T+240:

ECM1-240.GIF?08-12

A fascinating chart to start the day. A large and complex LP develops over SE Greenland over the weekend and dominates the week's weather keeping the British Isles in an unstable flow osciallating between colder and warmer airmasses as it moves first south and then east toward Scotland. By the weekend it is over or just to the east of Scotland but has filled considerably but is now drawing in a cold NNW'ly airstream so wintry showers for many with snow to high ground and some lower levels as well. Behind the LP strong signs of a rise in heights over Greenland propagating south into the mid Atlantic while the LP over Newfoundland meanders north perhaps bringinf some WAA over Greenland and re-enforcing the heights.

GEM 00Z OP at the same time:

gem-0-240.png?00

Fascinating chart number two. The remnant LP off the SW coast of Ireland is all that remains of a large deep and vigorous LP which at one point was 945 MB to the south of Iceland but the LP has filled and disrupted in the face of heights to the NE and faded away to the south.  A new pulse of cold air coming off the Eastern Seaboard of Canada is aligned negatively and a long way south but there is a growing cold pool over Scandinavia leaving the British Isles in a col. There's a SE'ly over the north but milder air hanging on in the SE. Could we see a big negative tilt to the trough ?

GFS 00Z OP at the same time:

gfs-0-240.png

And there's the hat-trick. As John Cleese would say "And Now for Something Completely Different". With GFS the LP doesn't get anywhere near the British Isles but disrupts far to the NW and so there's little to stop pressure building from the NE and we have a weak ESE'ly flow by this time with the HP centred over Norway. All I'll say about the rest of the OP run is I wouldn't look at it if you don't fancy cold.

GFS 00Z Control at T+240:

gens-0-1-240.png

Not quite there but nearly. A more vigorous Atlantic with a final LP trying to spoil the party and it might as it draws up the Azores HP but the Scandinavian HP looks fairly robust. However, further into FI the Atlantic wins out so a huge note of caution that we aren't there yet by any means.

Looking at the GEFS at T+240:

http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=240

The OP not without support but the problem is whether this final "tropical" LP heading NE will pull the Azores HP toward the UK and disrupt the E'ly flow.

In summary, the pattern change induced by events in the stratosphere moves ever closer and into range this morning. How it is being handled is varying considerably with ECM, GEM and GFS all in different places by the end of next week. Suffice it to say something is happening and the signals are clear but the manifestation tropospherically is still being worked out. Whether we see the Atlantic disrupt far away to the NW or to our south the clear signs for blocking to the NE are evident but whether it is transient or longer lasting is still to be resolved.

A fascinating time ahead for model watchers. 

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1 hour ago, johnholmes said:

A request please.

However great you think a post is please try not to include it all when it is a long one, simply give a link to the post.

thank you

 

And remember you can collapse a long quoted post by clicking the little down arrow at the top of the quoted post - saves an awful lot of scrolling.

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Sunday and Monday looking very interesting for the NW with very cold uppers and heavy snow showers. Showers possibly pushing well inland as winds turn more westerly.

sss.thumb.png.1669af1e527d78477d8fa8a66685f680.png

asfsffv.thumb.png.3443c1f013ecb8c5bc76fa4b2d870c39.png

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20 minutes ago, ICE COLD said:

Let's hope the GFS 6z is off the mark . 

IMG_1300.PNG

Which was my point about earlier buddy!!all these charts are fine at t300 but if theyre not gona get closer whats the point!!theres a higher chance of things going wrong!!only one run though so hopefully gfs 12z reverts back to cold!!to be honest its looking just as wintry and snowy for the next week so i think we should not forget that either!!

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19 minutes ago, ICE COLD said:

Let's hope the GFS 6z is off the mark . 

IMG_1300.PNG

And this is a reason people shouldn’t just think because we have a ssw taking place means cold and snowy for our little island. It all depends we’re the blocks ends up. Even with a ssw we could end up in a southerly flow. And wouldn’t that just be Sod’s law for us if that did transpire. 

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