Model thread discussion - cold spell looming

[southbank]

33 minutes ago, Paul said:

UKV 15z has shifted the Sunday prec a bit north, with some sizeable totals showing and signs of long reaching streamers..

 

For the following days, lots of showers packing into the east and quite widespread snow cover. Here's Monday as an example, but Tues and Weds follow suit with snow totals building. And hints of some snow moving up into southern areas on Tuesday as well. 

 

 

Thanks Pail for sharing these , totally appreciate you don’t have too but as the excitement builds it’s very very generous of you to do so - so thank you

[Sweatyman]

1 hour ago, Tim Bland said:

ECM snow depth for Sunday eve..

0.004 inch. Cant wait!

[Climate Man]

1 minute ago, Mike Poole said:

Interesting model output again tonight, I’m interested in what happens at T144, here GEM and ECM:

As modelled, no way that weak block will stop the Atlantic low or send it under.  But I wonder how much uncertainty there is about that low at this time?  I wonder if it might look weaker when it is at T96 in 2 days time?  

And after the mild interlude if it is an interlude, what next?  

I think I would like to have the cold air in place, tomorrow or Sunday, before trying to predict nature of the breakdown, and what happens afterwards.  

Spot on. The cold pool may well take some shifting and not be incorporated properly into the output.  

Expect big changes by Monday (hopefully)

[That ECM]

6 minutes ago, Sweatyman said:

0.004 inch. Cant wait!

You’ve read the chart wrong. You will get ten times that.

[Mike Poole]

ECM mean and spread T144:

The suite now suggesting some trough disruption on the incoming low, with some uncertainty too.  Not worth looking beyond T144 for the UK as the behaviour of this low is crucial for the way forward.  I’m not expecting any members to undercut this low yet, but they might in a day or two’s updates to the models...

Edited February 5, 2021 by Mike Poole

[phil nw.]

Any coldies would surely relish these charts for Monday.Bitter cold well established across the UK by then in a long draw easterly.One image shows the wind flow drawing that cold towards us from all the way from Russia.Fax for t72 alongside showing quite a stiff wind so it will feel bitter.

I would expect plenty of snow showers from this setup,especially the further east but with always the chance of a more organised area of snow anywhere if any small troughs develop in the unstable flow.
 

[JBMWeatherForever]

ECM is closer to how this will pan out come the end of the week. And not because it's a better outcome but because historically it has always been better at reading a breakdown   "if it happens" ?

[Battleground Snow]

ECM mean,

the op an outlier at the end, but a pronounced rise in 850mb temps 

[Yarmy]

The high-res ICON-EU 15z (yes, there is such a thing) is advertising an organised band of snow to head SW from Lincs/EA through the Midlands on Sat Night/Sun Mon (this is not from the main band of frontal snow on the low).

 

So a surprise for some on Sunday morning?

 

 

[Battleground Snow]

1 minute ago, Yarmy said:

The high-res ICON-EU 15z (yes, there is such a thing) is advertising an organised band of snow to head SW from Lincs/EA through the Midlands on Sat Night/Sun Mon (this is not from the main band of frontal snow on the low).

 

So a surprise for some on Sunday morning?

 

 

A few models have been showing this, but because it starts as rain accumulations are only modest.

[Snowboard Tennyson IOW]

1 hour ago, Man Without Beard said:

Worth a note - the extremely rare "channel streamer" sets up on the ECM on Tuesday - bringing snow to the most snow barren parts of the UK, South Devon and Cornwall, and possibly the IOW. Even the Isles of Scilly are in the sleet zone!

Where are the charts for this pls? Cheers

[Frosty.]

These ECM 12z ensemble mean charts have the power to make me gasp in amazement at their sheer beauty...now let’s get this party started!!!   

 

[Mike Poole]

ECM clusters T120-T168.

The fact that there are 6 of them should emphasise the uncertainty here, about any potential breakdown:

The key time is the T144, the middle column.  There are differences in the way that Atlantic low is handled, does it disrupt,  does it stall in place, or what?  I think this in FI for the moment, but will be firmed up in the next day or two, and could have a big impact on the next months weather.

Edited February 5, 2021 by Mike Poole

[Neilsouth]

15 minutes ago, phil nw. said:

 

 

Is that another occluded front heading towards EA and South East on Monday as well? Crazy stuff!

[SnowBlake]

48 minutes ago, That ECM said:

You’ve read the chart wrong. You will get ten times that.

You've also read it wrong, it'll be 100 times that!

If amount is accurate.

Edited February 5, 2021 by Blake Allen
Typo

[southbank]

Now that would be breaking news and worthy of a tweet

[stodge]

Evening all

Plenty of excitement as we look on the cusp of our most interesting spell of cold weather since March 2018 and the first spell of proper winter weather for many since 2013. I've posted on recent days how I've had doubts about the longevity and to an extent the severity of any cold spell. On Tuesday I was convinced it would be over quickly but by last night GEM and ECM were suggesting a more nuanced evolution which "could" keep colder conditions in place for some areas for longer. A lot depended on whether we would see height rises in Scandinavia sufficient to either hold the Atlantic at bay completely or deflect the troughs to the south east. 

I wasn't wholly convinced but nor was I convinced by the usual GFS trick of blowing up hurricane strength depressions to smash away any block. Yes, the PV is re-consolidating but it remains weaker than usual and that should give more chance for height rises to the north east - the process would be a brief milder spell before colder air returns again but under a drier and more settled evolution than we are set to experience in the coming days.

Let's see where tonight leaves us...

T+120 is Feb 10th, T+240 is Feb 15th, T+312 is Feb 18th and T+384 is Feb 21st.

12Z GEM: at T+120 an ENE'ly flow covers all parts with heights to the north and east and a residual LP over Northern Italy. The next Atlantic LP is far to the west. Uppers below -8 over most of the British Isles with -12 uppers in the North Sea. From there, the Atlantic LP comes up against developing heights to the North east but as it approaches and raises heights to the south it can only re-align north-south in mid ocean. Heights over southern Scandinavia are looking to join with heights over France and Spain leaving the British Isles by T+180 with a SW'ly flow over western areas and a SE'ly flow over eastern areas in the gap between the two weather systems. Positive uppers have reached western and some southern areas and further east 850s are only just below zero. From there, the HP declines south into Europe while the Atlantic trough remains far to the west. Mild or very mild air has crossed the whole of the British Isles by T+240 though it remains very cold far to the east.

We get about 5-6 days of cold out of GEM but the conversion to mild is straightforward as the Scandinavian heights simply collapse south. 1-0 to Mild.

12Z GFS OP - the T+120 isn't too much different to the GEM - an E'ly covers the British Isles and heights over Scandinavia face an Atlantic LP which looks to be aligning positively as a thin wedge of heights develops over Iberia. 85-s below -8 over most of the British Isles but milder air is already approaching from the west. From there, heights develop to the south while the Scandinavian heights remain in situ - the LP had elongated NE-SW with the main centre to the south of Iceland at T+180. While frigid air sits to the north and east, by T+180 the 850s are positive across most of the British Isles as the cold spell ends. From T+180, the Scandinavian HP is joined by the heights from the south and the new HP eases south as the LP moves north and east round the top of the HP over northern Scandinavia. By T+240, the HP is over Eastern Europe with new heights to the south west and the north west and a weak trough over the Faeroes. Less cold air with 850s either side of zero over the British Isles and the coldest air now further south east over the Balkans and Italy.

Only a 5 day cold period for most from GFS OP but the medium term evolution to T+240 looks more interesting than GEM and certainly a relief for those wanting some drier weather. 2-0 to mild.

12Z Control - No Parallel tonight so here's Control at T+120. As you'd expect, it's following the OP at this time pretty closely. From there, heights build over south west Scandinavia as the Atlantic LP eases towards Iceland leaving a SW'ly air flow across much of the British Isles. The progress of milder air is slower than on the OP with only southern and western areas in positive uppers and colder air hanging on in the north and east by T+180. The Scandinavian heights look to head south after T+180 but don't and by T+240 heights remain over central and northern Scandinavia but the coldest air is heading into the Balkans while the British Isles has a SE'ly air flow. On the mild side, uppers of +4 in southern parts but still just below negative in the far north and west.

Not dissimilar to OP and no sign of the Atlantic smashing through but we need th heights to set up more favourably so we get a sniff of the cold air rather than Greece. 3-0 to mild.

12Z ECM: the T+120 chart very much in line with other models and uppers below -8 for most if not all. From there, Scandinavian heights look to be developing kindly but by T+192 the HP has moved just too far south and a mild air flow is back over the British Isles with positive uppers for most northern and western areas. However, colder air remains close to the south east by this time but 850s are just negative. By T+240, the HP has slipped further south but maintains a ridge back toward the British Isles while shallow Atlantic LP run to the north and a hint of further upstream amplification is evident. 850s are up at +8 but that could be deceptive with some inversion possible. Hard to know at this stage. The colder air is now over the Mediterranean.

4-0 to mild by T+240. To be fair, inversion under that HP may not make it that mild in the south and east. The models have moved significantly away from powering the Atlantic through to building Scandinavian heights but the heights aren't sustained and collapse into Europe putting us on the mild flank of the HP. The Atlantic looks weak upstream.

Moving on, a look at the T+312 charts from OP, Control and P1:

  

There are a number of evolutions playing with the option of making the Scandinavian heights work and even retrogress (P1) and it'll be interesting to see if they gain more support in the coming days.

Conclusion: the initial 5 day cold snap/spell is set and it does look as show the cold will move away from Thursday onward and we then look but west but north east. All models are showing stronger heights over Scandinavia than was the case yesterday or the day before but for now the heights aren't strong enough and collapse from a potential high-latitude to a mid-latitude block which drags milder air back over the British Isles. At the moment, there is only minority support for holding the heights to the north east and perhaps retrogressing them towards Greenland - a real result for cold fans. However, that option wasn't even on the table a couple of days ago - let's see if it continues to gain ground in the next couple of days. A milder interlude looks unavoidable but it could be just that. For now, we have 5 days to enjoy and I hope everyone gets some snow - I think my chances in lowland East London are reasonable on Sunday and Monday but we'll see,

[East_England_Stormchaser91]

As expected, the ECM is calling for an extension already of the cold. Would not rule out more snow events to the SW before next weekend is out, given the volatility, and how much tomorrow and Sunday’s Synoptics are drastically correcting. 

[Scorcher]

2 hours ago, Cold Winter Night said:

Well, I keep my feet on the ground. I prefer the cold winter nights of my screen name, but I won't proclaim cold if that is an impossibility.

That 'energy', the lows into the Atlantic will not push through if the high is strong enough.
Day to day comparisons show Northern heights increasing for the same timeframe, i.e. models underestimated them earlier. So that milder interlude might not be as pronounced.

The best example of a cold spell that developed like this, December 1962. January '47 isn't far off either.

 

Regardless of whether the high is strong or not, the odds are strongly in favour of that Atlantic low getting close enough to the UK to introduce tropical maritime air. The ECM is now showing the same solution as the GFS, albeit slightly more delayed.

Another poster mentioned cold temperatures hanging on even in a warmer air mass if the surface flow is light- I can't see that happening in a setup like this one- looks a fairly strong SW flow to me, particularly in western areas.

[phil nw.]

7 minutes ago, Battleground Snow said:

ECM mean,

the op an outlier at the end, but a pronounced rise in 850mb temps 

Yes as we were saying earlier plenty of uncertainty of where this will go around day 6 on. A developing block stalling the Atlantic lows means the cold looks to be holding for a day or so longer and may well remain quite cold at the surface especially away from the south west.Ht anomalies day 8

Could get interesting again a little further on if the block gains more traction further north.There is still that cold block further east.

[TSNWK]

1 minute ago, Scorcher said:

Regardless of whether the high is strong or not, the odds are strongly in favour of that Atlantic low getting close enough to the UK to introduce tropical maritime air. The ECM is now showing the same solution as the GFS, albeit slightly more delayed.

Another poster mentioned cold temperatures hanging on even in a warmer air mass if the surface flow is light- I can't see that happening in a setup like this one- looks a fairly strong SW flow to me, particularly in western areas.

You would think so.  But there is also a slide from same ECM that has another Ice day for the vast bulk of England.  Pretty much as per green above

[Cavehill Snow]

1 hour ago, ICE COLD said:

Wow freezing still . They’ll be 7 to 8 days straight of ice days

I think the chart shows temperstures are for midnight.

[Paul]

The GFS 18z may be a bit delayed tonight, ncep having data dissemination problems again.

[CentralSouthernSnow]

15 minutes ago, East_England_Stormchaser91 said:

As expected, the ECM is calling for an extension already of the cold. Would not rule out more snow events to the SW before next weekend is out, given the volatility, and how much tomorrow and Sunday’s Synoptics are drastically correcting. 

I really hope so! Us south west people are so snow hungry 

[Djdazzle]

3 minutes ago, Paul said:

The GFS 18z may be a bit delayed tonight, ncep having data dissemination problems again.

You should get a job on British Rail!

Speaking of delays, it will be interesting to see whether the ECM 0z run continues the trend to extend the cold spell. Slightly stronger heights coupled with a shallower low could make a big difference.