Model Output Discussion: 12Z (20/11/12) And On...

[summer blizzard]

Models backing the cold west at day 8 with every run, -10 upper air profile now into Scandinavia..

[fergieweather]

Ps I'll come to the snow issue for early next week later ;-)

[TEITS]

Im not sure I agree with some of the comments referring to wintry weather in the model output. The synoptics may look impressive but the airmass isn't particularly cold. Any precipitation from the N/NE,ly is likely to be rain and I also doubt much convection would occur due to the lack of cold upper temps.

What has been consistent in the model output is the real cold remains bottled up to the N and so far I haven't seen a trigger to bring this S.

[bluearmy]

Ps I'll come to the snow issue for early next week later ;-)

thanks ian - dont forget any snippets re the seasonal meeting from yesterday (if you are permitted to share them)

[weather eater]

Good job then that the 12z's verify 500mb heights @ Day 6 as follows (and trust me, theres a bit of a surprise in the offing here):

http://www.emc.ncep....0_G2NHX_12Z.png

1. ECMWF

2. GFS

3. JMA <<<<< (spotted the surprise? Ian has mentioned the thoughts of MO regarding this previously)

4. UKMO

5. GEM

6. NOGAPS

SK

Absolutely, I was going to say while I rate the ECM over the GFS I can’t remember when the GEM and NOGAPS ranked above it. However this is the model thread and they are synoptic models so it’s perfectly legit to make posts about them and perfectly legit for anyone to say pull the other one.

And Crewe I have to say this to you, I’ve never been let down by model runs because I always view them with a degree of scepticism. I also suspect that some people are going to be let down anyway if they let their expectations run away from them over the next couple of weeks, because even with the pattern working out well, I don’t see snowmegedon in that time period. Besides the mother in law is coming up from Kent on Sunday for a week and I want her to be able to get back home again.

Edited November 20, 2012 by weather eater

[nick sussex]

Still the UKMO looks the odd one out in terms of that upstream phasing of those two lows. Big differences at only 96hrs between it and the ECM.

Great 120hrs from the ECM with that much more amplified ridge to the west, OMG this should be a great run and also those pressure rises to the ne.

Edited November 20, 2012 by nick sussex

[chris55]

We have enough problems looming in the next 12-48hrs without even pondering the longer term... 4KM modelled rainfall totals are troubling and we're also now changing warning emphasis to highlight strong pre-frontal winds Thurs; widely to 50kts inland with 60-65kts western exposures ahead of v squally frontal progression later that eve.

Oh I do like a good Squal line! Bren over on TWO used to give a heads up on an interesting Squal line approaching. I think the infamous "thundersnow" squall line back some years ago was the most violent one I have experienced.

[mcweather]

Posted Today, 09:01

NL, on 20 November 2012 - 07:51 , said:

Matt Hugo has mentioned heights to the NW/N of the UK diminishing around 2nd week of December with a return to zonal conditions.

Matt Hugo Stratospheric Watch thread.

The ECMWF 32 day update overnight as well maintains the signal for northern blocking through the 2nd week of December now with temperatures clearly becoming generally below average by a number of degrees. Without question, this excellent model, has nailed this situation down weeks in advance in terms of the broader change in synoptic pattern. However, what it now shows, is a return to more zonal conditions towards and beyond mid-December which is a concern. The +ve height anoms to the N and NW of the UK disappear by the 4th week of the run and are replaced by lower than average pressure anoms to the W and SW of the UK with temperatures recovering back to nearer average given a more unsettled theme.

To be fair Matt does then go on to say that after this more average zonal period it could potentially be turning colder again later into December... which is what happens even in the coldest of winters. We are unlikely to be in the freezer right through from the end of November to the end of February...

See also Terminal Moraine's very interesting response to Matt's comments on the Strat thread

So now let me think. mmmmmm.

A winter when December started coldish and blocked and then went more zonal in the third week before turning much colder later in the month.

Oh yes it was exactly 50 years ago run through the GFS karten archive and see for yourself

[latitude]

Im not sure I agree with some of the comments referring to wintry weather in the model output. The synoptics may look impressive but the airmass isn't particularly cold. Any precipitation from the N/NE,ly is likely to be rain and I also doubt much convection would occur due to the lack of cold upper temps.

What has been consistent in the model output is the real cold remains bottled up to the N and so far I haven't seen a trigger to bring this S.

There some lovely winter charts showing....just the missing the cold bit as you describe. As a newbie, at face value there arnt consistant (or any) -5 850's, so from my total ameteur perspective there wont be much snow about.

[swfc]

Another variation already on ecm????Low zips away,wheres this heading

[Tim Bland]

Epic ECM coming up! Ridge better, low cutting south of uk dragging v cold air down from the north. http://www.meteociel.fr/modeles/ecmwf.php?ech=144&mode=1&map=1&type=0&archive=0

[Zakos]

I have been watching the models very carefully recently and these are my thoughts on what is going to happen in regards to the upcoming cold spell, now that things have become clearer.

There is now definitely going to be some quite substantial PV disruption, heights are going to rise in the Arctic, perhaps quite significantly, and the AO will turn negative.There is also a fairly good chance that the Polar Vortex will completely split.

In terms of cold, we are too far out to decipher when it will arrive, or how cold it will be.

What we do know is that the weather is going to become more settled, as quite a substantial block builds in the Atlantic, cutting off the mild and wet Atlantic airflow.

After a spell of westerly weather, winds will swing to come from the north on the 27th. Snow is possible in the north and west of the UK, at least on high ground. This will not produce a widespread snow event to low levels.

After this brief northerly incursion, the block holds, centred close to Iceland,and winds then look likely to come from the E/NE, something similar to the image below

The continent is not yet cold enough to produce significant t850 values conducive for snowfall, especially with mild air from the Mediterranean getting into the flow. It will however be cooler than average at the surface

This is within the fairly reliable timerframe, and I am confident that this is how the weather will unfold for the rest of the month.

What happens after this is still unclear, however which such a favourable hemispheric pattern, I find it very difficult to believe that significant northern blocking will not take place very early on in December.

It has to be said, in terms of cold, nothing extreme is being shown..... yet. I firmly believe that once northern blocking sets up, we are going to experience a significant cold spell. It is impossible to predict how long it will last ; it hasn't even begun yet. In terms of snow potential and potency of cold, again it is pointless to guess until the block itself has set up.

Edited November 20, 2012 by Zakos

[SMU]

Look at the developing pressure towards NW russia..

Can we hijack that cold at day 10-12

S

[The Eagle]

Pretty good so far. Much colder uppers to the northeast.

[nick sussex]

http://www.meteociel...H1-144.GIF?20-0

Look at the developing pressure towards NW russia..

Can we hijack that cold at day 10-12

S

Any chance those weak lows near Svalbard could get sent packing allowing the Arctic high to ridge down or is that being greedy!

[Frosty.]

The latest GEFS 12z mean shows a colder trend throughout next week and out to T+240 with a large ridge held back out to the west of the uk and a trough over the eastern side of the uk with a cold NE'ly flow and unsettled with a wintry mix of ppn, the ECM 00z ens mean brings more settled weather to the north and west of the uk as high pressure looming large to the northwest begins to drift down over the uk slowly but it still looks rather cold and unsettled for SE Britain, so the question is, will it become more settled eventually with increasing amounts of sunshine but also widespread frosts as ecm shows or could we be looking at a cold cloudier outlook with NNE'ly winds and a trough to the east in control, so it's goodbye mild weather by the weekend, the air becoming more north atlantic sourced and then the airmass becoming more polar with time, eventually more continental, we really do need to wait for the plunge of arctic air to flood south through scandinavia and turn most of europe much colder and then hope we can get the synoptics to tap into that cold airmass, the next few days should give us the answers we are seeking, I noticed the latest meto is even more solidly behind the idea of a colder further outlook with frost, fog and wintry showers, now when they say wintry showers, that can easily mean snow showers aswell so fingers crossed for the early to mid december period to deliver a noteworthy cold shot.

[london-snow]

Posted Today, 09:01

NL, on 20 November 2012 - 07:51 , said:

Matt Hugo has mentioned heights to the NW/N of the UK diminishing around 2nd week of December with a return to zonal conditions.

Matt Hugo Stratospheric Watch thread.

The ECMWF 32 day update overnight as well maintains the signal for northern blocking through the 2nd week of December now with temperatures clearly becoming generally below average by a number of degrees. Without question, this excellent model, has nailed this situation down weeks in advance in terms of the broader change in synoptic pattern. However, what it now shows, is a return to more zonal conditions towards and beyond mid-December which is a concern. The +ve height anoms to the N and NW of the UK disappear by the 4th week of the run and are replaced by lower than average pressure anoms to the W and SW of the UK with temperatures recovering back to nearer average given a more unsettled theme.

To be fair Matt does then go on to say that after this more average zonal period it could potentially be turning colder again later into December... which is what happens even in the coldest of winters. We are unlikely to be in the freezer right through from the end of November to the end of February...

See also Terminal Moraine's very interesting response to Matt's comments on the Strat thread

So now let me think. mmmmmm.

A winter when December started coldish and blocked and then went more zonal in the third week before turning much colder later in the month.

Oh yes it was exactly 50 years ago run through the GFS karten archive and see for yourself

Just like to clear things up for those confused...

Although the 32 day model has picked the signal for colder conditions up a few weeks ago and has done very well this time around. There has been also times in the past where this model has been wrong so although rated caution is the order of the day especially when it shows a months worth of output ( Potential Breakdown ). A prime example of this was 2010 the cold arrived and despite signals and various outputs suggesting a breakdown the these charts stayed in fi for a long time and thus the cold continued further.

In these types of situations i am more inclined to follow the ecm op for the short and longer term and the ukmo short term and compare both in the short term range.

Hope that helps to some.

Edited November 20, 2012 by london-snow

[Nick F]

Epic ECM coming up! Ridge better, low cutting south of uk dragging v cold air down from the north. http://www.meteociel...ype=0&archive=0

Only looks cold in the north on the 12z ECM up to T+216, milder air dragged north over Europe getting in the mix further south as winds turn NE'erly then E'erly over the UK. We don't even get a countrywide cold northerly beforehand early next week like GFS, as the shortwave drops south further west.

Fantastic synoptics on the 12z ECM, but where's the deep cold air to tap into?

Edited November 20, 2012 by Nick F

[mcweather]

http://www.meteociel...H1-144.GIF?20-0

Look at the developing pressure towards NW russia..

Can we hijack that cold at day 10-12

S

The answer Steve is yes ( well just about)

[Continental Climate]

what an epic ECM chart couldnt have drawn it better myself http://www.wetterzentrale.de/pics/Recm2161.gif!! Thats what i call northern blocking

[Cheshire Freeze]

Only looks cold in the north on the 12z ECM up to T+216, milder air dragged north over Europe getting in the mix further south as winds turn NE'erly then E'erly over the UK. We don't even get a countrywide cold northerly beforehand early next week like GFS, as the shortwave drops south further west.

Fantastic synoptics on the 12z ECM, but where's the deep cold air to tap into? Granted we may has some dry shallow continental cold feeding in though.

If we can get through to the 216hr chart the cold will slowly back west with time. You can clearly see a retrograde pattern in evidence when you run through the 216-240hr frames. Those sub -8 850s edge slowly westwards, encroaching Scandi etc.

[london-snow]

Only looks cold in the north on the 12z ECM up to T+216, milder air dragged north over Europe getting in the mix further south as winds turn NE'erly then E'erly over the UK. We don't even get a countrywide cold northerly beforehand early next week like GFS, as the shortwave drops south further west.

Fantastic synoptics on the 12z ECM, but where's the deep cold air to tap into? Granted we may has some dry shallow continental cold feeding in though.

Agreed however 240 is looking very tasty to me..

ONE WORD = POTENTIAL..

Edited November 20, 2012 by london-snow

[cold snap]

sorry its keeps coming up.but after every run it needs to said.

850s and the lack off

[nick sussex]

Only looks cold in the north on the 12z ECM up to T+216, milder air dragged north over Europe getting in the mix further south as winds turn NE'erly then E'erly over the UK. We don't even get a countrywide cold northerly beforehand early next week like GFS, as the shortwave drops south further west.

Fantastic synoptics on the 12z ECM, but where's the deep cold air to tap into? Granted we may has some dry shallow continental cold feeding in though.

Yes it started so well and I had high hopes then it turned into mutton dressed as lamb! It looked good but a bit like one of those chocolates that look great until you bite into it and discover its one of those horrid liquer things people subject you to at Xmas!

The shape of that troughing is all wrong over continental Europe, we needed to see the elongated troughing further south and east to stop that milder air being pulled into the flow.

I think we're going to have to go the retrogression route to really deliver, hope I'm wrong but I just can't see any other way of advecting some deeper cold into the flow.

[Continental Climate]

sorry its keeps coming up.but after every run it needs to said.

850s and the lack off

I agree cold snap but you cant argue with the synoptics http://www.wetterzentrale.de/pics/Recm2401.gif!! This chart is like 1947 all over again a block stretching from southern greenland to western siberia