Winter Model Discussion 12Z 15/02/13 onwards.

[Jason M]

This run illustrates perfectly why the 850s matter.

Jason

[snow mad]

Don't like this run it lets the atlantic back in at 264hrs http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=264&mode=0&carte=1

[-uksnow-]

Fax's are out - 120hrs

Replica of UKMO output..

[Ice Day]

I was only posting last night that the pub run had been a bit low key this winter, then it goes and throws up a run like this! From 96 through to 192, one of the best runs for my region I've seen over the last few years. Highly unlikely it will verify like this, however the pattern is becoming nailed for a decent easterly that may last a few days or more!

[Stu_London]

What a bonkers 18z GFS run

Snowfest followed by 3 day thaw with maxes into the teens and right at the end of the run a rerun of Jan 1987

[Snowman.]

Wow

Europe getting a early start to 2013/2014 Winter

Just think if that landed on us....

This site would crash like it did with one those ECM runs....

[Gowon]

OMG!! GFS brings an even colder beast at 384

[Pembroke Dangler]

Has anyone got that old bbc weather forecast that Ian mcaskgill did back in the late 90's because synoptically the 18z gfs would produce that epic set of events surely! It won't happen I just keep telling myself but then again if it did wow could be said a few times this time next week

[Mair Snaw]

OMG!! GFS brings an even colder beast at 384

Quick somebody contact the Daily Express

[TEITS]

This run illustrates perfectly why the 850s matter.

Jason

Far to much emphasis can be placed on the 850s at times.

Since I joined this forum I have seen uppers as cold as -13C before. However the heaviest snowfall I have seen in the past 15 years occurred when 7 inches of snow fell in 4hrs when upper temps were at -2C and this occurred during Feb 2009.

I will add I wouldn't worry about the GFS predicted 2m temps. These can be way off at times and sometimes as much as 4C. Suppose the 18Z is right with its prediction of temps of 4C. Now under prolonged spells of sunshine that might be correct but under cloud cover and shower activity those temps would be around 0C instead. A good example is Dec 2009 when the GFS predicted max temps of 1C but the reality was -4C!

[Geordiesnow]

I have a feeling of apathy posting about the models at the moment hence the lack of my posts. This isn't because the output is poor because the output is stunning. My apathy is because on the face of it all models are similar at +120/+144 but when it comes to the actual weather on the ground they are very different.

The exact placement and orientation of the HP won't be decided for another 48hrs just yet and this will impact the extent of the cold plus snowfall via convection. Now if the 18Z GFS is still showing the same output on Sunday then I shall be posting frequently with plenty of excitement.

I agree, whilst in many respects, the models are not all that far away from agreement, there is differences still which could mean big differences to the weather we actually experience.

I think the mostly likely is that the outlook will remain dry and it would not surprise me if a Northerly comes into play more in the next few days and the easterly gets shorter as past experience seems to go when the models show these set ups.

[Captain Shortwave]

Pure unadulterated perfection, that would be pretty much 5 days of potential snow for many areas. The important thing is whether the ensembles support the idea of troughing to the south supporting a easterly flow which will bring in the deep cold or whether the setup starts sagging and we get a more tepid south easterly.

GFS, UKMO and GEM all support this easterly idea with ECM not developing really any low heights to the south up to the Atlantic undercut

Of course we probably won't get something as special as this but if we get low heights over Spain/Italy early on then we have a good chance

Edited February 15, 2013 by Captain shortwave

[PolarWarsaw]

The problem with runs like this? People will actually consider them coming to fruition. They dont and wont. So the eventual outcome will be watered down regardless - it can't be considered a downgrade on runs like this. So when the 0Z shows nothing like this - please dont bring the prozac out.

[Dave Kightley]

Epic run...Never known 0z to ever repeat it though..Bring on thesnowfest in the south west

[Snowman.]

Of all the runs this winter this is BY FAR the best.

89 Days of winter =

356 GFS runs.

178 ECM runs.

178 UKMO runs.

Of all them this is by far the best starts cold we have a VERY NICE easterly then breakdown before a reload from the East, two cold spells in one GFS both being better than what we have seen this year.

[phil nw.]

Well the GFS 18z goes on to exemplify the best possible result from that holding pattern to the NE with perfect snergy to allow the cold pool west at the perfect time that the right weight of energy undercuts from the atlantic. For the second half of Feb it doesn't get much better!

Absolutely!

I know it`s has the tag of the Pub run but it isn`t far away from the pattern depicted by the 500hPa ens hts over the last few runs.

The high is trending further west with time -as suggested in those forecasts.

Maybe the 850`s will be less cold come the time but even allowing for some modification of those the pattern as shown would be as good as we could hope.

Just to add whilst not a bad run for cold i was a little surprised at the way the ECM run sunk the High SE somewhat in it`s later frames which was against the trend of those forecasts-which are still similar this evening btw.

Edited February 15, 2013 by phil nw.

[Tamara]

This run illustrates perfectly why the 850s matter.

Jason

It depends - early on, as the High to the NE establishes, we depend on the upper cold advection and instability to generate potential snow showers (with hopefully increasingly less marginality as time goes on with this process).

However once the continental flow gets established and especially as the airstream is constricted by approaching frontal systems, then accelerated despatch of very low dewpoint and surface cold from the continent replaces the need for deep cold uppers. The examples though the years prove this connection. The Feb cold spell of 1978 arrived though very similar mechanism to this with snow showers in the north and east initially with the deepest cold air, but the heaviest and most disruptive snow, as depicted by members earlier this evening, arrived in the far South and South west at the arrival of the frontal masses. They were buried in snow with upper temperatures at onset not much below freezing as the fronts battled to make inroads - and failed .

Edited February 15, 2013 by Tamara Road

[Tom Jarvis]

Didn't someone say on the last thread that the 18z verifies better in the shorter then that the 12z. Which would mean this could happen as the minor details are now appearing in the shorter time frame??

[LomondSnowstorm]

It depends - early on, as the High to the NE establishes, we depend on the upper cold advection and instability to generate potential snow showers (with hopefully increasingly less marginality as time goes on with this process).

However once the continental flow gets established and especially as the airstream is constricted by approaching frontal systems, then accelerated despatch of very low dewpoint and surface cold from the continent replaces the need for deep cold uppers. The examples though the years prove this connection. The Feb cold spell of 1978 arrived though very similar mechanism to this with snow showers in the north and east initially with the deepest cold air, but the heaviest and most disruptive snow, as depicted by members earlier this evening, arrived in the far South and South west at the arrival of the frontal masses. They were buried in snow with upper temperatures at onset not much below freezing as the fronts battled to make inroads - and failed .

Yes, numerous classic examples of 'get the cold in and the snow will follow'. Once you've had the cold uppers to start with then provided there's no maritime airmass modification it really does take a lot to budge precipitation type from snow to rain.

[TEITS]

I shall finally add that in my opinion the UKMO is wrong and im totally amazed the fax charts back this.

If you take a mean of all todays outputs from every model then at +120/+144 the UKMO is too far S with the position of the HP and the pool of cold air. My prediction for tomorrow is the UKMO will be further N tomorrow and as a consequence the Met O forecast will be changed from wintry showers to snow showers pushing inland.

[Gowon]

Quick somebody contact the Daily Express

No we better not!

Hopefully it's a new trend for pressure to rise again around Scandinavia....

[cooling climate]

Would not be at all surprised in seeing the Euro models repeating something similar

to the the 18z run upper temp wise in the next day or two.

[Jason M]

Far to much emphasis can be placed on the 850s at times.

Since I joined this forum I have seen uppers as cold as -13C before. However the heaviest snowfall I have seen in the past 15 years occurred when 7 inches of snow fell in 4hrs when upper temps were at -2C and this occurred during Feb 2009.

I will add I wouldn't worry about the GFS predicted 2m temps. These can be way off at times and sometimes as much as 4C. Suppose the 18Z is right with its prediction of temps of 4C. Now under prolonged spells of sunshine that might be correct but under cloud cover and shower activity those temps would be around 0C instead. A good example is Dec 2009 when the GFS predicted max temps of 1C but the reality was -4C!

I agree with this for the most part. I don't think this is one of those times where they don't matter though. It's absolutely nailed on that its going to be cold IMHO but the 850s in this scenario are the difference between slate grey skies and a constant temp of plus 2c for a week and heavy convective snow showers.

I agree completely re the ground temps. I actually think we might squeeze a couple of ice days out of this. The extra solar input might actually be useful inland as under a cold pool some pretty violent snow showers could kick off.

For me, this evolution has strong support within GEFS so given the range it has a real chance IMHO.

Jason

[Froze were the Days]

Crazy run but haven't we been here before...in early December first with the GFS and then the ECM jumped on board big style and then the GFS jumped off. In my mind the UKMO is similarish to the GFS at around 144+ but the UKMO profiles the HP 300 miles or so further south with just the far south tapping into the cold uppers.

Overall the 12z's and this run has improved the overall situation and all 3 are on a similar wavelength but as TEITS mentioned small variations in placements and orientation of the HP can make a big difference, still along way to go even though 120z is almost in sight.

[steelermark]

Probably the only thing worse is the posters that feel the need to bang on about those that are supposedly banging on about it being dry. For the benefit of those willing to learn, your evidence to debunk this supposed myth is?

Actually many years of reading this forum with people going on about it showing dry when in fact we end up with inches of the white stuff on the floor just a few days later. The 18z proves that trying to work out precipitation this far out is pointless. It's anything but dry on that run!!

I wasn't banging on about it either, I mentioned it once unlike the people talking about it being "dry".