Model output discussion - winter proper underway

[karyo]

29 minutes ago, feb1991blizzard said:

Might as well throw this in there as well then, pity we cant see a breakdown of months.

Is this the GLOSEA or another model?

[feb1991blizzard]

1 minute ago, karyo said:

Is this the GLOSEA or another model?

Yes GLOSEA5.

[feb1991blizzard]

Actually @Man With Beard  The ECM does give some modest accumulations midweek but very localised for the Pennines, but I think the ECM snow accumulation charts are as fanciful and certainly exaggerated as some of the GFS FI extreme solutions.

[Paul_1978]

3 hours ago, Broadmayne blizzard said:

According to a recent  poster in the Southwest regional thread. 

Fergie quoted as saying Glosea going for blocked Jan and the model is also keen on strat warming event late December/early Jan.

Not in so many words! 

See the Model Tweets thread. 

[karlos1983]

Few cold runs being thrown into the mix now..

[The Enforcer]

2 hours ago, ArHu3 said:

 

The thing that interests me about that link is for all the obsession with SSWs, there are plenty of years without them where significant snowfall still occurs - two examples being one of the very snowiest winters 1995/1996 and the potent Feb 1991 easterly.

[East_England_Stormchaser91]

The FI stages are no different to ones assumption realistically talking. To the here's and nows, the temperature is currently set to plummet to minus double digits tonight for some areas, with a smaller milder interlude and then another potential snow event for a few with some less potent northerlies returning. 

Following on from that, the progress, dynamics and alignment of the jet will be one to watch as we are on knife edge territory between what could be winds from the mildest direction available (SW) and then the coldest direction available (E/NE) given the time of year and depending on if we see sufficient height rises over Scandi into Russia. It's these sorts of situations where I've seen the models flip most. Early 2013, FI always had the idea of a default zonal pattern until we saw just what could be classed as a marginal raise in heights to our NE, and that still managed to deflect the pattern south, which changed the prospects dramatically. Feb 2012 was another similar example. 

[feb1991blizzard]

28 minutes ago, The Enforcer said:

The thing that interests me about that link is for all the obsession with SSWs, there are plenty of years without them where significant snowfall still occurs - two examples being one of the very snowiest winters 1995/1996 and the potent Feb 1991 easterly.

but late jan 1991 was as good as one though.

[Cheshire Freeze]

2 minutes ago, feb1991blizzard said:

but late jan 1991 was as good as one though.

Also depends whether you've got the strat or trop running the show. It's possible to maintain a fairly decent disconnect. However, more often than not, you won't get HLB with a very cold strat. 

[feb1991blizzard]

1 minute ago, CreweCold said:

Also depends whether you've got the strat or trop running the show. It's possible to maintain a fairly decent disconnect. However, more often than not, you won't get HLB with a very cold strat. 

I have never looked at the strat profile of 96 winter but have been through the trop pattern hemispherically on meteociel many times right from autumn to spring and looks to me like everytime the zonal westerlies downwelled, there was an amplified trop pattern to just stop them enough to buy more time, rinse and repeat right the way through.

[Cheshire Freeze]

2 minutes ago, feb1991blizzard said:

I have never looked at the strat profile of 96 winter but have been through the trop pattern hemispherically on meteociel many times right from autumn to spring and looks to me like everytime the zonal westerlies downwelled, there was an amplified trop pattern to just stop them enough to buy more time, rinse and repeat right the way through.

Exactly. 

Which is why I was urging caution a couple of weeks back RE the trop amplification subsiding and letting the pattern flatten out. 

[Guest]

WINTER 2017/18 REPORT No. 4b WITH DECEMBER 11th INPUT

PART 2: With my main weekly reports tending to be quite long, I shall continue to split them into at least 2 parts probably posted several days apart. This one will be in 3 parts. As they can take many hours to prepare, this will enable me to draw more on the most recent model runs rather than earlier ones. Part 1 (on page 7 of this thread) reviewed the model output and looked well ahead for any early signals of a possible second cold spell. This part includes an update of my European indicators and analysis and part 3 (tomorrow or Wednesday) will focus on my Arctic indicators.

It seems an age since I last looked at the European and Asian temperature profiles and snow cover indicators. In fact it was only 8 days ago in part 2 of my third winter 2017/18 report (on page 126 of the 1.9.17 Autumn model thread). With all the excitement surrounding our current cold spell and a significant widespread snow event, perhaps one can be excused for overlooking the fact that much of Europe has also seen some pretty severe weather with storm force winds in France and Austria. There are some interesting changes which I’ll examine later in this report.

A “Possible” Easterly Some Time after Christmas - What Can We Expect?

I promised in part 1 of this report that I would take a closer look at the conditions that we might expect should we see an easterly air stream over this country. I have been looking for any signs in the model output of height rises to our north-east. Despite what a few posters have said, I feel that I have already provided some "early stage" evidence of this in the late (obviously unreliable) parts of a few of the model runs during the last couple of days. Please refer to my two recent posts on page 7 and page 11 of this thread which demonstrate this evolution possibility. Before I go any further, I must provide my usual warning.

CAUTION:  Nobody should be under the illusion that I am definitely predicting that we shall have a significant cold spell let alone an easterly. There have been “hints” from our specialist teleconnection posters (such as @Tamara, @Glacier Point, @chionomaniac and @Catacol amongst a few others) that the background signals are currently conducive to a renewed positive PNA following a temporary negative phase during the next week or longer (for those interested and wishing to learn, I see that @Quicksilver1989 has posted an excellent definition of what the PNA is – on page 12 of this thread). This positive PNA would probably lead to increased Atlantic and Arctic amplification (perhaps assisted by the MJO moving into the key phases of 7, 8 and 1) and tentative indications of a build of pressure to our north-east. The timing of these changes (if they happen) remains uncertain and the less cold or mild interlude (there are still some recent model runs holding the Atlantic back for longer at the start) following the current cold spell in the run up to Christmas could last rather longer than a week, possibly through to the New Year. Things can easily change and they will be the first to tell us if they see these signals change (fade or strengthen) or a different outcome or evolution is indicated. Yes, I am a self-confessed coldie but I would never wish to mislead anyone. For much of this report I am merely examining the outcome and impacts of the possible cold evolutions – in this part, an easterly and part 3, further northerlies.     

It is one thing achieving the right synpotics to produce an easterly but there are other hurdles to overcome. Easterlies have been so rare during the last 25 years or so, that it’s easy to forget that they do not always delivery deep cold and in fact, that they are more likely to be dry rather than snowy. Back in the 1960s to 1980s they were so much more common and we often saw at least one or two easterly spells even in the milder winters.

The rarest easterly of all is the one with a very long fetch all the way from Siberia. That requires HP ridging from Siberia, through northern Russia and into Scandinavia. I did a post (on page 134 of the 1.9.17 Autumn model thread)  comparing some of the 1962/63 winter to the current winter (please do not assume that I’m ramping up a possible repeat!!!). I described some of the weather patterns with charts for the most interesting episodes. Perhaps, many on here will be surprised to learn that that epic winter hardly had any periods with a long fetch easterly! In fact the deep cold for long periods was confined to much of Europe and the UK, with most of Asia as well as North America having a very average to mild winter. Apart from frequent Arctic incursions, the predominant pattern was a polar continental one which fed a cold pool which developed over central and western Europe including the UK. There were regular slider low events which helped in renewing the deepest cold with the flow from mainland Europe. These often came in on a short fetch easterly or south-easterly. This was one of the best examples of manufacturing our own “home-grown” cold pool with a little help from Europe which is quite achievable (given the right set-up) this time of winter with the sun so low in the sky. That was a case of get the right pattern established, get the cold in and give it a chance to stagnate and deepen in situ (nearby HP or a slack pressure gradient would be required). Perhaps we can include a cold pool co-operation clause in our Brexit negotiations!

Some easterlies develop when the continent has been relatively mild. Whilst I cannot remember any warm easterlies in winter, I can remember some with normal temperatures and quite a few more with only rather cold conditions with no snow and no frost, just cold rain and drizzle. More often than not easterlies are cold or very cold. The longer they persist the more likely they are to pull in some increasingly cold air. Much depends on the source conditions. Milder air can move into the easterly flow from the south. Many easterlies are dry. It depends how close we are to the HP, whether any disturbances form in the air stream or whether Atlantic frontal systems can move in and perform an undercut – a number of significant and historic snowfalls have developed in these situations (often with uppers above -4c but with sub 0c dew points). Convective easterlies require much lower uppers (sub -8c) to produce snow showers as the air stream picks up moisture as it crosses the much warmer North Sea.  Part of my European and Asian temperature analyses in this and future reports will bear in mind the various possible easterly scenarios. 

British Sea Surface Temperatures:

            December 10^th 2017                       December 2^nd 2017                      December 10^th 2016                       December 10^th 2015  

                                      

The recent frequent northerlies and the cold spell have helped to lower the sea surface temperatures around the UK. They are generally another degree lower since my Dec 2^nd report. This is also partly due to the lack of strong south-westerlies as well as the normal decrease from the summer to the winter months. I also show the charts for the same dates for the last two winters. Remember the second half of November and early December last winter was also colder than average but early winter 2015 saw very mild south-westerlies following a rather cold and anticyclonic spell in October (where it started off with lower sea temps than this Autumn). Compared to the last two winters at the same stage, this winter has seen slightly lower sea temperatures around our shores more especially in the North Sea.

European 2m Surface Temperatures:

                Dec 11^th 1450                                 Dec 11^th 0650                                     Dec 2^nd 1450                                   Dec 2^nd 0650     

                                                       

Note that it is important to allow for min/max temps when comparing the charts. The 0650s are usually close to the minimums and the 1450s are usually close to maximums when other conditions remain similar.  Much of western Europe has warmed up in the last 2 days while the UK has remained cold. Scandinavia is little changed but notice  the purple colours in north-west Russia - this is considerably colder than it has been recently.

Northern Hemisphere Temperature Charts:

               a) Current – GEFS 18z T+0 for 1900 on Dec 11^th :                                   b) GFS 12z T+6 for 1900 on Dec 2^nd:  

                   2m Temps                                        850 temps                                           2m Temps                                           850 temps

                                      

The key change in surface temps is the expansion of the area of sub -32c to sub -40c temps over Siberia and northern Asia and a band of sub -20c temps heading steadily south-westwards through Russia and getting closer to Europe. Until the last few days, much of central and western Russia had experienced unusually warm conditions, so this is a very welcome change. Scandinavia has also seen a fall in temps.  There are some pockets of cold but there is currently no real sign of a cold pool over Europe. If the milder interlude develops over the UK next week as generally predicted, I will monitor how far these conditions penetrate into Europe. Much of the cold may well be pushed much further east. Should the much colder conditions in Russia persist, then this pool will be available to tap into later on. I will comment more on this as well as the 850s in next week’s update.

Asian and European Snow Cover:

I show animations for snow cover and sea ice changes. These are produced by the National Ocean and Atmospheric Administration (NOAA).  When you go to their site you can change the date range and go back over 10 years. You can change the speed and pause on any particular day. You can also switch to a northern hemisphere view. These are brilliant, very informative charts and great to play around with. I’ve re-set the link below to show the period since my last report from December 2^nd to December 11^th but you can change the dates on the site and choose your own options.

Animated Europe and Asia Day Snow Cover  (updated by NOAA December 11^th):

https://www.ncdc.noaa.gov/snow-and-ice/snow-cover/ea/20171202-20171211

                        December 11^th chart:                                      December 2^nd chart:

                                                        

North Asian snow cover has been well above average since mid-October. During the last few days, the widespread snow cover there has extended further south, south-east and particular south-westwards. Scandinavia now has a complete snow cover. The snow cover in Europe has been much more inconsistent and come and gone several times. Nice to see some snow cover in the UK and a fair portion of England - no further comment required!

In Conclusion:

There is a cold pool over northern Asia and this has extended through Russia during the last few days. This looks like it might hang on and will be available to tap into “if” we do start to see height rises to our north-east in several weeks’ time. Given the current Russian temperature profile, a cold pool could develop over Europe quite quickly if HP ridges westwards from Siberia and/or Russia. I will be updating my Arctic indicators in part 3 (due out either Tuesday or Wednesday).  

Finally, while I was writing this report, I see that the ECM 12z was badly received by many posters and given a rough ride on this thread during this evening.  As I said in my post on page 11 (regarding the warm looking end to the ECM 0z run), this is not as bad as it might seem to a coldie! It’s important to focus far more on the northern hemisphere charts rather the Europe view. You can see the PNA going positive again and just starting to ridge into the Arctic and it looks like this is set to link up across the Pole to the stronger HP on the Siberian side. T+240 is only 10 days away and still well before the possible reamplification period. We are looking for “very early” signs of this change and these may well come and go on successive runs for the next few days at least.

I also see that the MetO 15 to 30 day forecast has pushed back by a few days the period for a pattern change to something more settled and colder. This is still well within the “around Christmas to early January” window that has been hinted at for renewed blocking and building heights to our north-east. Continuing patience is the message and let’s keep looking for any evolving trends. 

 

Edited December 12, 2017 by Guest
Correct typos and check charts

[Snowy Hibbo]

EC Weeklies

Week 1 (12-18 Dec)

UK is under control by a Euro/Scandi low and an Atlantic ridge.

Week 2 (19-25 Dec)

UK is under ridging anomalies, with ridge extended well into Atlantic.

Week 3 (26 Dec-1 Jan)

UK is under troughing anomalies for the Inter Holiday period, with troughing across the Atlantic.

Week 4 (2-8 Jan)

Still troughing anomalies over Atlantic, extending over the UK.

 

Summary: AO is rather neutral/slightly negative for Week 1 & 2, but goes towards a more -AO setup in Weeks 3 & 4.

UK troughing on Weeks 1, 3 & 4.

-EPO/+PNA present through to Week 3.

 

 

 

[Snowy Hibbo]

3 hours ago, feb1991blizzard said:

Might as well throw this in there as well then, pity we cant see a breakdown of months.

Probably should add the EC Seasonal anomalies to that.

January

February

March

You can kind of see a somewhat similar pattern, with some troughing over Canada in Feb/March, and the UK in January. And over the Atlantic throughout. Interesting times. What is also interesting is ridging anoms around the Aleutian region.

[feb1991blizzard]

9 minutes ago, Snowy Hibbo said:

Probably should add the EC Seasonal anomalies to that.

January

February

March

You can kind of see a somewhat similar pattern, with some troughing over Canada in Feb/March, and the UK in January. And over the Atlantic throughout. Interesting times. What is also interesting is ridging anoms around the Aleutian region.

TBH I never like troughing to the W of UK as an anomaly, Those charts just scream mild wet to me, I prefer low anoms to the south.

[KTtom]

Some pretty dire output overnight, including the longer term models, difficult to find anything to support the east/west battle which many of the experts were promoting for later in the month.  Strange how quickly the trend can go from cold to mild, wet and windy. Let' hope the models pick up on a signal soon to revert back to something more blocked for the end of the month...otherwise I have a horrible feeling the topic of conversations will be around flooding!

Edited December 12, 2017 by KTtom

[Dennis]

Scandi is trying late December

[mulzy]

Pretty awful NWP output this morning. Knocker and Sidney must be thrilled!!

Is there any light at the of the mild tunnel?

Edited December 12, 2017 by mulzy

[carinthian]

Morning all. This mornings GFS run holds back the full throttle mild invasion into the UK again. Looks like not giving up its cold hold without a fight, Chart below keeps cold surface flow at day 10 .

 

[mb018538]

Hmm, things don't look too great from my own point of view:



Looks like this may take a while to shift!

[snowbunting]

1 minute ago, mb018538 said:

Hmm, things don't look too great from my own point of view:



Looks like this may take a while to shift!

Hopefully I have read the chart right! It does for a while but not convinced its grip will be maintained in January looking at the two areas of low pressure around the Greenland and Siberia.the colder less dense air looks for prone to lobing and spilling out of the arctic than normal. Any SSW will pretty much destroy any strong vortex fornation. I think the words vulnerable and potential are appropriate here.

 

 

[robbo88]

What are people's thoughts on the chances of this happening tomorrow night? I get it is the Gfs and it overplays snow.

I am not very good at reading charts so I can't tell what the conditions would be on ecm.

But the regional forecast also mentions rain turning to snow? 

[JamesL]

1 minute ago, robbo88 said:

What are people's thoughts on the chances of this happening tomorrow night? I get it is the Gfs and it overplays snow.

I am not very good at reading charts so I can't tell what the conditions would be on ecm.

But the regional forecast also mentions rain turning to snow? 

It's something the Met Office are keeping a close eye on as the system moves SE there could be snow to low levels during tomorrow's rush hour in the NW. High ground could see quite a depth. 

[Troubleatmill]

5 minutes ago, robbo88 said:

What are people's thoughts on the chances of this happening tomorrow night? I get it is the Gfs and it overplays snow.

I am not very good at reading charts so I can't tell what the conditions would be on ecm.

But the regional forecast also mentions rain turning to snow? 

100% accurate i would say, it has a small patch of green right over my house, amazing accuracy

[Paul_1978]

One straw I can grasp this morning is a comparison to winter 1990/91:

Major December snow event - check (remember Dec 1990!)

Milder period after that. (Check out Christmas Day 1990, yuk). 

And keep your fingers and toes and everything else crossed for another Feb 1991!

The output is not great at the moment if it's cold your after but without wanting to go over old ground there are still a few straws to clutch in various places. 

Edited December 12, 2017 by Paul_1978