Model output discussion - Into 2021

[Penrith Snow]

Just another word about Uppers, despite all the gloom and forecasts of sleety rain which were made on Christmas day,  I have now recorded 3 ice days and 2 days with moderate snowfall in the last week.

This morning moderate snow was falling across East Cumbria with surface temperatures of -3c and uppers of -6c, needless to say the snow was of the dry, powdery nature and a long way from the sleety rain that was promised!  

I think we need to reconsider what are the requirements for snow in the UK as it clearly isn't simple and not get hung up on modest Uppers.

Andy

[swfc]

Second snowfall here today, that's twice in a week. Anyway given the fluidity of the mo I wouldn't look to far ahead. Nhp and tpv on its knees so sit back and enjoy

[mountain shadow]

3 minutes ago, Penrith Snow said:

Just another word about Uppers, despite all the gloom and forecasts of sleety rain which were made on Christmas day,  I have now recorded 3 ice days and 2 days with moderate snowfall in the last week.

This morning moderate snow was falling across East Cumbria with surface temperatures of -3c and uppers of -6c, needless to say the snow was of the dry, powdery nature and a long way from the sleety rain that was promised!  

I think we need to reconsider what are the requirements for snow in the UK as it clearly isn't simple and not get hung up on modest Uppers.

Andy

Indeed, for on the other side of the coin, it is  positive 6 degrees here at 500 feet with those same -6 uppers having been in a Northerly airstream for nearly a week.

Evaporative cooling in heavier bursts is the winner at the moment.

[sebastiaan1973]

2 hours ago, chionomaniac said:

I have had a good look at the strat charts this morning and there appears to be a lot of guesswork as to how the SSW may affect the trop.  All indications to me are that we have a good propagating event already in the early days after the SSW.

One would expect normally a flushing down of westerly winds to the trop and therefore an increase in a flatter trop pattern for a while. But to me this is just not happening. This is the picture as of yesterday:

We have the weakened residual positive u winds at the top to middle strat about to be crushed by the developing SSW. What is of particular interest here, is the fact that prior to the SSW, the middle to lower strat positive u winds are either very weak, or on the case of the troposphere, none existent. These (strong) lower strat winds would normally act as a barrier to propagation, or will be flushed down trop wards as the SSW takes hold. But as they are not present the SSW can propagate right down to the trop almost ‘unopposed’.

So by day10 we have this:

The whole polar field from strat top to trop bottom almost one complete negative anomaly. Not only is it likely that the quick propagation of the SSW will continue to deliver a more meridional NH trop pattern, but where cold is transported south to mid latitude areas the cold will likely be severe and long lasting. The effects of this SSW are likely to be felt for some time yet, probably til spring.

What we can’t be sure of yet is how we are likely to be affected, though early indications suggest a continuation of the winter pattern we have seen so far. But with cold reinforcements added in for good measure.

 

edit - just to explain that u winds are mean zonal mean winds at any given latitude and height.ie where when travelling around the earth at say 60°N and 10hPA height, the net winds are positive (westerly) or negative (easterly)

Well. In my opinion there is first an increase of westerlies in the lower parts of the Atmosphere. As shown in 144h.

[Methuselah]

Just now, mountain shadow said:

Indeed, for on the other side of the coin, it is  positive 6 degrees here at 500 feet with those same -6 uppers having been in a Northerly airstream for nearly a week.

Evaporative cooling in heavier bursts is the winner at the moment.

The very same over here, MS... rain here, sleet there, snow somewhere else -- most places nothing: must be almost a textbook definition of 'marginal'?

[markw2680]

What I really don’t understand is the fascination of always looking into deep fi? If you look at all the models for the next few days or so they continue to show cold weather with snow chances along the way, if you continue to look into deep fi it will be a very very bumpy ride unless of course it’s that what you like. Or of course it could be to purely look for hope of mild just to wind people up?
who knows just a bit odd in my book.

[Man With Beard]

40 minutes ago, Cold Winter Night said:

Many nervous posts these days about Ops at day 10 and ensemble means at day 14. As if a day 10 chart is as reliable as a day 3 chart.

Everybody keep in mind that the reliability goes down rapidly as you go further ahead in time.
Adapt your expectation level accordingly.

Great chances of cold and snow at +24h? Be very excited, not much can go wrong.
Great chances of cold and snow at +72h? Be excited, with a tiny bit of caution.
Great chances of cold and snow at 168h? Sure, fun to watch, but stay calm and be aware that the ECM correlation of 500hPa heights is only around 80%, so placement of highs and lows may change considerably. In our favour, or against it.

Below the correlation of 500hPa heights at 3, 5, 7 and 10 days. Good to see that ECM improved over the years, but day 10 charts have a long way to go before they reach 100% (they never will).

It would be nice though if everyone got at least some snowflakes just to calm the nerves as we await the main event.
Here in Holland I haven't seen snowflakes since Feb1, 2019 and the last time I went skating was in 2017.

Great chart - so 80% ECM accuracy at D7 but 50% accuracy at D10 ... tells us a lot about which charts to take seriously.

Does anyone have recent stats for ECM ensemble mean? I thought they had better verification, something like 60-70% accuracy, but I may have remembered wrong.

[Scott Ingham]

8 minutes ago, mountain shadow said:

Indeed, for on the other side of the coin, it is  positive 6 degrees here at 500 feet with those same -6 uppers having been in a Northerly airstream for nearly a week.

Evaporative cooling in heavier bursts is the winner at the moment.

We had powdery snow off light precipitation off of -6 uppers mate.

I have 3cms. Its surprised me how far on marginal we actually are but not having an omshore breeze has a lot to do with it

[Scott Ingham]

Volatility.

Key word.

No cold spell is de-railing

Nothing is getting flusued in my opinion as theres nowt to flush

Just remember that as we see the 12s run. Relax and let the models make sense of something ir rarely has to model.

Btw im in such a good mood after the second decent snowfall in a week here in White Rotherham!!!!

[Updated_Weather]

Hope 12z shows something for my area in Essex - had absolutely nothing so far!

[Battleground Snow]

Small but noticeable improvement on the icon as early as 72 ,both the high into Greenland and the cold pool to our North east looks slightly colder

Nice band of snow moving down the country right now looks more organized than modelled.

 

Edited January 2, 2021 by Battleground Snow

[Blessed Weather]

Further to Polar Maritime's post above, I am moving the discussions about the odds of a SSW impacting the UK to the Moans/Chat thread as they are not discussing current model output.

And for the record, folk may wish to note this quote from Grahame Madge of the Met Office which is currently being widely reported in the media. Just paste the quote into Google to find the articles.

"Two out of three SSW events result in very cold episodes, but one in three has little impact at all."

[Chesil View]

So here’s a thing, over the past week or so both the gfs and the ecm have tried to flatten or de-amplify the pattern  but then had to correct that aberration.  With no real west to east energy in the current set up could it not just prove to be another aberration that will have to be corrected with time.  Just a thought..

Edited January 2, 2021 by Broadmayne blizzard

[Frosty.]

I was pleased with the ECM 0z ensemble mean, much better than the op which had a toppling high followed by less cold, the mean showed entrenched cold and more snow potential...ps..another wintry update..I’m much happier than I was last winter..and the winter before that..etc..etc..as I’ve said before, there is huge potential for the kind of winter coldies have been craving and we just haven’t had for several years now..fingers   ️ !!

Edited January 2, 2021 by Jon Snow

[SMU]

Good Afternoon

ICON improves with more cold over the UK ( sub -6 ) but also a negative tilted high in the atlantic & less 'warm' pocket influence from that low over benelux

[DanDorsetUK]

Given I don't normally take day 10 charts to seriously especially so at the moment with the impending SSW everything we are seeing needs to be taken with a very large pinch of Salt. 

After reading through all the posts from PV-forecast on Twitter it's safe to say the Northern hemisphere is staring down the barrel of a very large event. They are calling this an extreme event.

Given the speed in which this is developing it should start to show very quickly in the models similar to 2018. They are stating there is much more heat than was being predicted. For anyone who's not looked through there Twitter posts it's well worth the read.

Obviously this does not mean we will get the extreme cold but given the longetivity of the event I quite rate our chances.

The signs in the models will become very obvious to see and very quickly when they do. This SSW points to extreme cold spilling into the lower latitudes. And for once I actually have a good feeling were in for quite a ride.

[Battleground Snow]

Icon 144. Looking great.

Cold heading in from the north

Edit: blows up the low at 168

Edited January 2, 2021 by Battleground Snow

[ancientsolar]

GFS 12z time !!  

[SMU]

ICON key > good with the greenland heights > probably a bit over blown on the low... 

[Scott Ingham]

6 minutes ago, Battleground Snow said:

Icon 144. Looking great.

Cold heading in from the north

Edit: blows up the low at 168

Big move back towards that west based Greenland high there though.

I await the rest of the 12z with a lot of interest!

[Scott Ingham]

Just now, Jason M said:

Had some 'potential snow' here this morning. Its a bit like real snow but cunningly disguises itself as rain .

Hahaha! It was magical this afternoon here mate!

[Brocken Spectre]

This makes a good read whilst waiting for the next runs.  The Model Thread and the run up to TBFTE after the 2018 SSW event.  It's interesting to see how the models handled it and the posters!! Model forum post 2018 SSW

Edited January 2, 2021 by Brocken Spectre

[winterof79]

2 minutes ago, Scott Ingham said:

Hahaha! It was magical this afternoon here mate!

METO on back foot over mid month warm up.Lets see if UKMO agrees

[Scott Ingham]

5 minutes ago, winterof79 said:

METO on back foot over mid month warm up.Lets see if UKMO agrees

I genuinely think well be looking at systems trying to push in very sluggishly creating battleground snow before the cold wins out mid month

Having now just read the updated meto forecast they think the same.

Big upgrade in wording that!

Edited January 2, 2021 by Scott Ingham

[Howie]

30 minutes ago, Broadmayne blizzard said:

So here’s a thing, over the past week or so both the gfs and the ecm have tried to flatten or de-amplify the pattern  but then had to correct that aberration.  With no real west to east energy in the current set up could it not just prove to be another aberration that will have to be corrected with time.  Just a thought..

Yes, the high that is amplifying now was originally being modelled to topple over us if I'm remembering correctly