Model output discussion - deep cold inbound?

[I remember Atlantic 252]

Just now, kold weather said:

Closer view for you:

This is 6am on Sunday.

clearly see the cloud shield, FAX surely has whole setup further SE, meaning convective showers anywhere

[kold weather]

4 minutes ago, I remember Atlantic 252 said:

clearly see the cloud shield, FAX surely has whole setup further SE, meaning convective showers anywhere

I'm honestly not sure what the person doing the fax charts is seeing, I've not seen a single model as far SE as they've placed it tonight. Then again I'm not trained in this regardless of experience lol!

Especially given the UKMO/UKV and to a lesser extent ECM place the frontal shield further NW - Unless there is a very large precip shield which maybe possible given the amount of moisture picked up over the North Sea.

Then again that is for 12z and the whole lot may have sunk southwards by that time?

Edited February 4, 2021 by kold weather

[Frosty.]

Some of tonight’s ECM 12z ensemble mean charts made me gasp in awe...stunning for a mean!...even Mr Spock was mildly impressed!  

plenty more gasping in awe to come during the days ahead, tons more eye candy..crucially, within the reliable timeframe rather than deep FI!!..Enjoy my fellow coldies!

  ️  

[sparky1972]

2 minutes ago, kold weather said:

Closer view for you:

This is 6am on Sunday.

oh joy, perfectly placed for no snow, lol,  but to be fair thats what been forecast for a cpl of days now, but, seriously, there is going to be some great snowfall for some peeps here, lets hope the models show us all getting in on the act during the week, everyones opinions make great reading.

[DAVE_ALLEN]

19 minutes ago, carinthian said:

Latest fax charts moves the frontal activity away with remnants of any milder air from the SE more quickly on this chart on Sunday. The bonus being the air mass will be much colder in the circulation , hence I think a upgrade for snow potential in the SE of England for Sunday of a convective type.

C

Theres the smallest HP ridge there from Birmingham to S Ireland.  If anywhere was to see less snow on Sunday I would imagine it would be here. And Essex and Kent by contrast would have a snow upgrade if this fax materialises as shown

 

[carinthian]

5 minutes ago, kold weather said:

Whats odd about the UKMO fax charts is both the UKMO 12z run AND the UKV are much more aggressive with the snowfall and place the fronts much further NW than that location.

Interesting to see the differences, not sure what has made them place the fronts there, its not really backed up by anything that we can publicly see at the moment.

 I think KW the duty forecaster will have seen that the UKMO model have uppers at 850mb of -4c on Sunday and lowering to nearly -10c on Monday. So that kind of cold air advection more likely to occur on clearance of any frontal zone.

C

[carinthian]

3 minutes ago, DAVE_ALLEN said:

Theres the smallest HP ridge there from Birmingham to S Ireland.  If anywhere was to see less snow on Sunday I would imagine it would be here. And Essex and Kent by contrast would have a snow upgrade if this fax materialises as shown

 

Hi Dave,  streamers can penetrate quite far west with a Easterly component. Nay impossible to be 100% sure. Obviously further east the greater chance of snow but never say no 1

 C

[Griff]

1 minute ago, Griff said:

 

I know, wrong thread, but almost certainly of interest here... 

[kold weather]

7 minutes ago, carinthian said:

 I think KW the duty forecaster will have seen that the UKMO model have uppers at 850mb of -4c on Sunday and lowering to nearly -10c on Monday. So that kind of cold air advection more likely to occur on clearance of any frontal zone.

C

Its quite cool to watch the UKMO, because the front obviously gets quite the undercut on the UKMO, this is the exact same time as the charts I posted of the UKMO earlier:

Of course as you say once the front clears even colder upper temperatures flood across the region, which does make sense as to why they'd place it further south I suppose.

However whats odd about the fax charts is there is still a reasonable amount of precipitation along the frontal boundary and its still sitting broadly in the same location as it was, heres 18z:

I'm not really sure the frontal shield would be that far north if the front really as far SE as the fax chart is showing?

My only ideas is it could  be that we've actually got a load of embedded north sea convection in that 18z chart above and the frontal boundary is indeed further south which would make sense if the front is as far south as that fax chart suggests.

Then again I'm sure they've got the details to make a better call old armchair forecaster me haha!

Edited February 4, 2021 by kold weather

[londonblizzard]

23 minutes ago, Tim Bland said:

You do know these are upper air temps...about 1500m up

Yes ofcourse, 3 straight days with a -9 to -10 uppers mean seems great to me for this part of the country, especially when we have been teased with milder sectors on various runs for a number of days now. I accept that later on in the chart is a bit disappointing for people after longevity 

[phil nw.]

26 minutes ago, Mike Poole said:

ECM mean and spread T240:

Mean looks conducive to some heights to the north into Scandi, and potential for atlantic lows to go under.  Think there is actually a case even on the mean for average easterly winds in the NH bar the top of the chart, and of course the Atlantic!  Spread just shows massive uncertainty, reinforces message FI is T96, anything after that you are relying on background signals or tea leaves, in my case background signals though, and they are good, so expect upgrades in the T144-T240 timeframe.

Yes Mike the mean Atlantic pattern is very close to it's op by the looks too.

It's also possible that the Atlantic makes partial inroads only into to the sw quarter with a snow event to the north of the boundary before being pushed back.Possible snow/rain/snow event somewhere even and all snow north of that.I have seen that before.Signs indeed of a possible Scandinavian pressure rise leaves plenty options wrt future evolution.

Looking at the ens temp graph the further north we look at those the colder the uppers show at day 10, so signs that the cold will not give way easily,especially at the surface under any ridging following. 

[Tim Bland]

4 minutes ago, londonblizzard said:

Yes ofcourse, 3 straight days with a -9 to -10 uppers mean seems great to me for this part of the country, especially when we have been teased with milder sectors on various runs for a number of days now. I accept that later on in the chart is a bit disappointing for people after longevity 

Apologies, I though you were referring to the possible longevity / extension of the cold spell. I agree , Sun- Thurs looks great, hopefully some classic snowy scenes in the city early next week

[carinthian]

3 minutes ago, kold weather said:

Its quite cool to watch the UKMO, because the front obviously gets quite the undercut on the UKMO, this is the exact same time as the charts I posted of the UKMO earlier:

Of course as you say once the front clears even colder upper temperatures flood across the region, which does make sense as to why they'd place it further south I suppose.

However whats odd about the fax charts is there is still a reasonable amount of precipitation along the frontal boundary and its still sitting broadly in the same location as it was, heres 18z:

I'm not really sure the frontal shield would be that far north if the front really as far SE as the fax chart is showing?

Could it be that we've actually got a load of embedded north sea convection in that 18z chart above and the frontal boundary is indeed further south?

Then again I'm sure they've got the details to make a better call old armchair forecaster me haha!

 It is of course possible that the fax chart has been simplified until the higher resolution outputs from the snow computer come in to real affect 48 hours before a snow event. At the moment we are still 72 hours away for the SE at least but the latest fax drops the fronts into the continent on Sunday.

C

[rdt123]

Can anyone shed some light on this ? When I look at the 12z uppers from Sunday onwards look to be quite severe for the north east. I’d also expect quite a lot of activity from the North Sea in the stuff easterly breeze. In anticipation I have had a look at the met office forecast for Stockton on tees and it shows mainly light sleet showers ? How can that possibly be right ? Which model is producing that output ?

rob

[GeordieX9v]

Just now, rdt123 said:

Can anyone shed some light on this ? When I look at the 12z uppers from Sunday onwards look to be quite severe for the north east. I’d also expect quite a lot of activity from the North Sea in the stuff easterly breeze. In anticipation I have had a look at the met office forecast for Stockton on tees and it shows mainly light sleet showers ? How can that possibly be right ? Which model is producing that output ?

rob

Snow is notoriously hard to predict more than a day in advance mate I wouldn't worry. I would imagine any showers that do pop up in the north sea would have the chance to be thundery.

[kold weather]

4 minutes ago, carinthian said:

 It is of course possible that the fax chart has been simplified until the higher resolution outputs from the snow computer come in to real affect 48 hours before a snow event. At the moment we are still 72 hours away for the SE at least but the latest fax drops the fronts into the continent on Sunday.

C

I think the problem has been solved looking at the 15z UKV in full for the next 24hrs thanks to Nick F in the region thread.

Its indeed what I wondered about.

The frontal boundary weakens and then does move south, but almost instantly a strong convective outbreak happens which effectively fill the gaps left as the front slides southwards, maybe a trough formation develops where the frontal system was previously sometime in the afternoon and helps to feed in activity into the SE?

It definately looks convective on the UKV though past the morning.

[Tim Bland]

6 minutes ago, carinthian said:

 It is of course possible that the fax chart has been simplified until the higher resolution outputs from the snow computer come in to real affect 48 hours before a snow event. At the moment we are still 72 hours away for the SE at least but the latest fax drops the fronts into the continent on Sunday.

C

What is the ‘snow computer ‘ you refer to that the Met will use for the fax? Do they not just use all high res models such as UKV & Euro4

[bluearmy]

Extended eps hint at an easterly again later week 2 and the clusters are indeed around 32% supportive although the main cluster is the polar opposite (ie. not polar at all!)

from little acorns .....

[I remember Atlantic 252]

1 minute ago, kold weather said:

I think the problem has been solved looking at the 15z UKV in full for the next 24hrs thanks to Nick F in the region thread.

Its indeed what I wondered about.

The frontal boundary weakens and then does move south, but almost instantly a strong convective outbreak happens which effectively fill the gaps left as the front slides southwards, maybe a trough formation develops where the frontal system was previously sometime in the afternoon and helps to feed in activity into the SE?

It definately looks convective on the UKV though past the morning.

So no frontal shield right over the Midlands, I know a lot can change up to 12 hours before the event

[Mike Poole]

22 minutes ago, rdt123 said:

Can anyone shed some light on this ? When I look at the 12z uppers from Sunday onwards look to be quite severe for the north east. I’d also expect quite a lot of activity from the North Sea in the stuff easterly breeze. In anticipation I have had a look at the met office forecast for Stockton on tees and it shows mainly light sleet showers ? How can that possibly be right ? Which model is producing that output ?

rob

You should get plastered eventually, here the Arpege take on it, and remember it won’t fully account for convective snow:  You can really see the easterly take hold on this!

Newbies, notice how the precipitation changes from organised areas to linear streamers as the convection starts...

 

Edited February 4, 2021 by Mike Poole

[phil nw.]

Back to closer at hand for Sunday by which time according to the t 72 fax and ukv models the beast is fully in the house.A stiff and bitter easterly embedded across the whole country showing north of the occlusion.

Any rain in the far se looked short lived earlier in the day on the ukv output and soon turns to snow.

Bitter cold -10/-11c uppers widely by then with -13c uppers heading across the n.sea.This will spawn snow showers and possible streamers over the following couple of days with the air becoming more unstable as it crosses the water with the large temperature difference.

I wouldn't be surprised to see short term warnings as we go along as the high resolution models pick up on any further disturbances in the flow.

I would say this is a proper beast now with those upper temperatures -10c and lower with source of cold from way east in N.Russia.

Edited February 4, 2021 by phil nw.

[kold weather]

1 minute ago, I remember Atlantic 252 said:

So no frontal shield right over the Midlands, I know a lot can change up to 12 hours before the event

If there is a really active area down there as per the UKV there will be some suppression to the north for a short time as the frontal cloud shield won't go away too rapidly, especially if its being filled in anyway by a larger area of convection, so may still have a similar effect for a time.

I'd think eventually that area will weaken, especially once the low weakens and then overnight into Monday you'd get a more classic distribution again.

That'd be my guess! Again, I have to say, these are only guesses and these things have a habit of moving around quite some way even just 48hrs out.

EG it could still end up quite a ways north, or indeed struggle to clear France on the way up.

[carinthian]

3 minutes ago, kold weather said:

I think the problem has been solved looking at the 15z UKV in full for the next 24hrs thanks to Nick F in the region thread.

Its indeed what I wondered about.

The frontal boundary weakens and then does move south, but almost instantly a strong convective outbreak happens which effectively fill the gaps left as the front slides southwards, maybe a trough formation develops where the frontal system was previously sometime in the afternoon and helps to feed in activity into the SE?

It definately looks convective on the UKV though past the morning.

Yes, I remember a similar situation when I worked at Gatwick. Can produce hours of snowfall over a relative narrow zone. Would be hard to predict.

C

[SqueakheartLW]

Some great 12z's showing up for cold. I shall go over the two usual 12z models as always

GFS 12z

Can the GFS maintain its sub -10 850hpa temperature average at the peak of the cold spell after both the 00z and 06z did. The peak on this 12z comes at 138 hours away

Still showing an average easterly but due to this peak coming near the end of the cold spell on this run then less of a beasterly element by this stage. However the 850hpa temperature average on this run was again sub -10 as it came in at a nice -10.3 which is -7.4 below the long term mean. Now over to the 18z then to complete the day with a full set of sub -10 runs. The anomaly chart maintains those deep blues over the UK too.

GEM 12z

The GEM delivered its coldest so far in my updates earlier with its 00z run at -10.0 at 850hpa. Can the 12z also deliver and give us a GEM -10 party. The peak of the cold spell on the GEM 12z comes at 126 hours away and good news is that this 12z is a new coldest so far and matches the 12z GFS with another -10.3 at 850hpa which is -6.9 below the long term mean. A nice set of GEM runs today and with much less scatter now in the colder period this now looks more odds on to happen.

[carinthian]

9 minutes ago, Tim Bland said:

What is the ‘snow computer ‘ you refer to that the Met will use for the fax? Do they not just use all high res models such as UKV & Euro4

Hi Tim, I am not sure but the guys will be on the ball with the present situation. Possibly just a case of now casting over the coming days.

 C