Model output discussion - here comes the beast!

[Frosty.]

There's still tons of uncertainty from the end of the week but I think the models are backing away from the milder trend compared to last night and what an incredibly wintry week ahead..it's going to be HISTORIC..I'm so excited!

Edited February 25, 2018 by Frosty.

[nick sussex]

It may or may not turn milder by next weekend, before that there is some quite exceptional cold shown for this late in the winter, and plenty of snow chances.

Theres also the possibility of a big snow event as the low to the sw moves ne, the margin for error even if every model agrees at day 5 is enough to markedly change the conditions on the ground for parts of the UK.

So my advice just wait and see what the trend is over the next few runs. 

[MattStoke]

To say you can't see how the models could be wrong 5 days out is ridiculous.

[Weathizard]

I'll take a PTB1 please ? It's bizzare but it's  the best of the bunch

[Speedbird]

10 minutes ago, Reverse Zonality said:

The only thing I can suggest is you check the ensembles on ECM and GFS. There is huge spread after Thursday which is why jumping to conclusions after every op run is a pointless exercise. 

 

the voice of reason . . . 

[Sainsbo]

I feel like we're giving a little bit too much attention to the 850hPa temperatures for the event on Friday. The colder uppers seem to be easily pushed aside by the low, but with 4-5 days of temperatures struggling to get above freezing and harsh night time frosts the boundary layer is going to be extremely cold.

Whilst the 850hPa temps could possibly become "mild" in comparison to what we will experience this week, the warmer air associated with the low will probably be pushed aloft to an extent with the surface temperature staying around or below freezing. If not snow, counties in the far south would probably see some freezing rain.

[stratty]

2 minutes ago, Frosty. said:

There's still tons of uncertainty from the end of the week but I think the models are backing away from the milder trend compared to last night and what an incredibly wintry week ahead..I'm so excited!

Yes Frosty, I agree. Just flicking through the ensembles for next weekend shows the uncertainty, some just bring slightly colder air meaning copious amount of snow nationwide. You can see why some weather forecasters have a serious look in their eye while presenting atm! 

[SMU]

Just the first signs that the GEFS not so keen to move the warmth North- More of an attempt North before stalling & moving East - PTB 2 for example...

As highlighted though it will probably go to T24-48 etc

S

[Derecho]

More runs backing milder air by the weekend on the 06z. Far from a done deal given the knife edge synoptic situation later in the week but I'd like to see the trend go the other way....

[Buzz]

I think the problem that most people have with Weathizard's assessment is that he's saying it's " game over for the south/far south ", he then presents the main models for day 5 as evidence for this.

Naturally most people want the cold (and snow) to continue, there is also understandably a certain degree of hope-casting, BUT we need to bear a few things in mind:

a) How many times have we seen the models reach a consensus for 5 days hence, only for them to be wrong? Quite a number I'd say, particularly where snow is concerned

b) Bearing in mind the timescale and also the added complications of the SSW this leaves the model output even more open to question than usual

c) The various model outputs overnight/this morning has already seen some corrections for the less cold air not getting as far north as modeled yesterday

d) We're only looking at small changes in the flow and position of the low for the precipitation to fall as snow, even in the far south

e) I don't think that we'll have this nailed down even by Thursday, it could well be a now-casting event

If Weathizard's assessment wasn't so cut and dry (and accepted that there is room for error) then all would be well.

 

Edited February 25, 2018 by Buzz

[Pembroke Dangler]

I just can’t see that low moving from directly south to north it will have some easterly movement to it surely sending centre of the low into north France and Belgium that’s how I see it going.

[nick sussex]

1 minute ago, Steve Murr said:

Just the first signs that the GEFS not so keen to move the warmth North- More of an attempt North before stalling & moving East - PTB 2 for example...

As highlighted though it will probably go to T24-48 etc

S

I think the NAVGEM has got it right ! 

 

[Summer Sun]

06z Short ens for London showing it staying very cold until around Thursday then the control, op and mean all agree on slightly less cold air for the weekend ground temps on the other had will take longer to respond

[winterof79]

Meanwhile back at the ranch.......

And that's before the second push of really cold and the tightening of the isobars

And yes that is Arpege ,which for the sake of your sanity,is a good bet as it doesn't run into la la land and probably nearer the mark for the METO 

Edited February 25, 2018 by winterof79

[SnowBear]

Sometimes I feel too many take weather models as gospel, it's going to happen. They only show what "might" happen with varying degrees of accuracy depending on the complexities within the weather systems at the time.

With the current set up for the coming Friday onwards is quite complex, small shifts in the track of the low (I won't use correction, it's completely the wrong word to use), the depth of cold on land, amount of snow cover remaining plus many other variables make for it to be almost impossible at this time to predict what will happen, but the models give us a range of possible outcomes.

Some time ago on here and now when I find time I followed and did Hurricane tracking, it taught me a lot on predictions, potentials, and possibilities within computer models. I suggest maybe some would like to participate later this year in some Hurricane tracking? Tracks and conditions changing hour by hour, sometimes in even less timeframes?

Models are an aide into predicting but not the absolute.

[Summer Sun]

Full London ens on the 06z a fraction lower than the 00z around the 7th obviously seeing a repeat of the -15's is probably unlikely but still on the chilly side

00z

06z

Edited February 25, 2018 by Summer Sun

[WalsallWeather123]

Had a look through the GEFS Pertubations and there is a very fine line between prolonged cold and milder air mixing in. This won't be resolved until T24

[Catacol]

5 hours ago, Argyle1980 said:

Regarding Friday. UKMO & ECM both marginally better this morning from last nights viewings. As it’s been said, been a little too progressive in removing the cold uppers so quickly and I think a trend of correcting further south is on the cards.

Morning all - ‘twas a very odd day yesterday... Scotland giving England a good shoeing at Murrayfield which was unexpected, and then an unexpected flip from the models to a much milder scenario.

But I think this post will be proved right. We have often seen models pick up on a fresh signal or trend, run with it hard for a run or 3...and then slowly backtrack to some kind of half way solution. Think I would therefore agree that Fridays low will not penetrate far enough north to ruin any northern snow cover but will get close enough to the south to create the high risk high gain scenario @chionomaniac referenced the other day. I still hang my hat on the observation that models frequently are over progressive in this kind of scenario anyway.

So nudges to the south this morning followed perhaps by further nudges on the 12z and all will remain good. MetO certainly don’t seem to have blinked - I wish we had access to Mogreps....

House chores now... but will take a wider look at signals later. Very exciting week is now only hours away..

[AmershamMike]

32 minutes ago, Frosty. said:

There's still tons of uncertainty from the end of the week but I think the models are backing away from the milder trend compared to last night and what an incredibly wintry week ahead..it's going to be HISTORIC..I'm so excited!

I can tell!!! Enjoy it Frosty - always find your posts a breath of fresh air, especially recently!! Keep it up mate!!

[bluearmy]

Thickness watch:

Ec and gfs : T90/T96. 504 dam crossing Scotland. Small area ne england T90

 

[stodge]

Morning all

No detailed analysis from me as Mrs Stodge has other plans for my Sunday.

Just a few comments on the output I'm seeing this morning:

1) The threat of a west-based negative NAO has always been there - I was talking about it at the beginning of last week. We needed a much stronger HP profile than we are now seeing to firmly the deflect the Atlantic LP more east and south. This is how the 2010 cold spell ended (and in fairness was superbly modelled by GFS which nailed the evolution consistently from T+384 down).

2) Bringitback62-63's excellent summations did take me back to March 2013 when GFS consistently modelled the return of warmer air from the south west for it to fail time and time again. I'm less convinced of the parallels this time but it's worth bearing in mind.

3) Many have agonised in the past week over the exact positioning of the cold pool which varied by 150-200 miles from run to run - now we are agonising over an LP where the scale is similar. As others have said, exact tracks and trajectories won't be clear until Wednesday but the NAVGEM solution would, I suppose, be many people's preference. I wouldn't be surprised to see less cold air cross the country over next weekend.

4) It's unrealistic to expect -12 uppers to be over us for weeks - the coming 72-96 hours will be an exceptional spell for many (and a predictable disappointment for some) but inevitably it couldn't last and even if we had managed a seamless transition to a NE'ly (which never looked likely) there would have been an easing in the frigidity of the air.

5) Once again we are seeing signs of height rises to the east and north-east in far FI - not inconceivable we could have another Scandinavian HP by mid month and certainly one to watch. It's entirely possible while this week's cold may be the most severe, it won't be the last.

One thing is certain - more exciting and tense model watching this coming week as there has been in the past fortnight watching the cold spell evolve.

[Johnp]

29 minutes ago, nick sussex said:

I think the NAVGEM has got it right ! 

 

Wouldn't it be amusing if a combo of Icon and NAVGEM nailed this cold spell ?

[bluearmy]

by day 5, we will have shoved an area of very  low thicknesses into the Atlantic just sw of Ireland. This is not normal. To expect the nwp to deal with it effectively is quite an ask. I am actually  a little surprised that nearly all the modelling is on the same page here. I note that some 06z gefs members begin to vary on whether this deep low will actually exist by Friday or if it may actually end up a disrupting lw trough. 

We wont have a cold block over the uk in the traditional blocking high sense. We will have very cold air in situ. 

Let’s see if we are in the same place come tomorrow’s 12z output. 

[captaincroc]

15 minutes ago, Johnp said:

Wouldn't it be amusing if a combo of Icon and NAVGEM nailed this cold spell ?

I was thinking this before that the IKON really was the king of the models in preparation for this spell. Did someone say it was to do where it specialised in the atmosphere?

[Frosty.]

Looking at the GEFS 6z mean, first of all the easy bit..nationwide severe wintry spell developing in the next few days from the east and lasting most of the week..by next weekend it's still cold, very cold further north and it continues cold further ahead, especially across scotland until almost mid march, becoming less cold further south but I wouldn't call it mild!!..and the trend, compared to last night's milder 18z mean appears to be to keep the cold for longer so hopefully that will continue and we could yet all end up staying predominantly cold / very cold for the foreseeable future!

Edited February 25, 2018 by Frosty.