Model Output Discussion

[chionomaniac]

GFS ensemble mean is opening the door for a significant snow event, roughly t200 through t300 on current programming for southern UK and t200 - t360+ further north.

This is t264 but it's a good representation of a deep trough to our east filtering cold air south and south-west, and low heights right across the Atlantic allowing lows to approach from our south-west as the core upper ridge shifts towards Canada and western Greenland:

http://raleighwx.eas...nomalyNH264.gif

Projected 850s at this time are well below average:

http://raleighwx.eas...nomalyNH264.gif

Operational ECM guidance is very similar.

Based on Global Wind Oscillation composites, the evolution towards this west based -NAO will take some time and there may be a case for current model guidance being too progressive with an Atlantic low swinging in. With the AO likely to become strongly negative, a Scandinavian trough looks very sustained which will mean the cold puddle of air over NW Europe will take a lot of shifting. The snow threat from next weekend onwards should not be underestimated.

Hear, hear GP. Taking everything into consideration I feel that this set up is looking so encouraging that it may surpass that of January for many areas. The positioning of the Scandi trough which is likely to drop towards the UK is vital and this week could just be the starter in preparation for the main course next week! If -15ºC 850"s hit some part of the UK before the end of February I would not be surprised (20-40% chance) and that is purely based on the outlook not on a ramping basis. I have always thought that getting that -ve NAO may be delayed because of the slow splitting and retrogression of the displaced vortex.

c

[Mark Bayley]

but that is for 17th Feb its miles and miles away before then. i know it's a bit of a bugbear of mine. but why look past the next 3-5 days? blimey, the models have struggled past 48 hours in the recent past. let alone get it right for 10 days away.

sorry, not having a go at you. just can't see why people look so far ahead. (even Met O only goes to T+144)

I did say don't look far ahead as it will change :lol: The idea of high going north westwards looks a pretty safe evolution.

"wouldn't worry to much at this stage. There will be many evolutions over the coming days. I remember GP saying a west based NAO was likely, which then opened the risk of attack from the South West. We shall just have to watch the models over the coming days. The high retrogressing north westwards seems very likely after the initial easterly."

[nick sussex]

The ECM and UKMO look better this evening whilst the GFS after carrying the baton for so long decides to drop it metres from the finishing line!

It's funny now the euros increase the potency of the easterly the GFS decides to bring in a slacker flow.

Overall though some good output, although in the latter timeframe it would be good to see the models edge the block further east to stop the Scandi trough from coming too far west.

[Thundery wintry showers]

I think thawing during the daytime is very likely early in the week with maximum temperatures between 3 and 5C- this will tend to cause some thawing of snow cover regardless of how much sunshine there is, especially as very few places can expect much snow on the ground to begin with. Towards the back end of the week, if this easterly comes off, we should see maximum temperatures near freezing and a more widespread/significant snow cover which should make it far more resistant to thawing in sunshine.

We have reached the time of year when a thin snow cover tends to melt in the sun even with low temperatures because as soon as a hole is punched in the snow cover, especially over concrete surfaces, the sun heats up the surface and accelerates the thaw in surrounding areas. But a reasonably thick snow cover tends to reflect solar radiation making the sun less of an issue.

[chionomaniac]

The ECM and UKMO look better this evening whilst the GFS after carrying the baton for so long decides to drop it metres from the finishing line!

It's funny now the euros increase the potency of the easterly the GFS decides to bring in a slacker flow.

Overall though some good output, although in the latter timeframe it would be good to see the models edge the block further east to stop the Scandi trough from coming too far west.

That is probably the biggest risk as the -NAO converts more to a west base. This chart suggests that we are perfectly positioned in the UK before that occurs:

[MAF]

I did say don't look far ahead as it will change The idea of high going north westwards looks a pretty safe evolution.

yes mate :lol: wasn't having a go. and just to put me in my place GP then posts a post for next weekend where he seems to have a lot of confidence. i shall go back to just reading the model threads and not posting in them me thinks :lol:

[Joe Bloggs]

The ECM and UKMO look better this evening whilst the GFS after carrying the baton for so long decides to drop it metres from the finishing line!

It's funny now the euros increase the potency of the easterly the GFS decides to bring in a slacker flow.

Overall though some good output, although in the latter timeframe it would be good to see the models edge the block further east to stop the Scandi trough from coming too far west.

Hi Nick, it should be noted that the 12z GFS op is actually a bit of an outlier in that respect...

Looking at the control run for instance http://91.121.94.83/modeles/gens/run/gens-0-1-132.png?12 , looks very good for a potent easterly, as does the majority of the ens members.

Mean - http://91.121.94.83/modeles/gens/run/gens-21-1-132.png?12

The ECM and UKMO look better this evening whilst the GFS after carrying the baton for so long decides to drop it metres from the finishing line!

It's funny now the euros increase the potency of the easterly the GFS decides to bring in a slacker flow.

Overall though some good output, although in the latter timeframe it would be good to see the models edge the block further east to stop the Scandi trough from coming too far west.

[Mark Bayley]

yes mate wasn't having a go. and just to put me in my place GP then posts a post for next weekend where he seems to have a lot of confidence. i shall go back to just reading the model threads and not posting in them me thinks

You had a valid point though, many of us look to far ahead a times, especially when there's a lot of interest in the short term! Great post from GP, keeping in line with the high retrogressing North Westwards. Will be interesting see how the models handle this over the coming days. I know some concerns have been raised about it becoming to west based (-NAO) That would open up the risk of an attack from the South West. Which i think GP was mentioning with the snow risk greatly increasing, especially with the colder air over us. Will go back and have a read

Still, some snow showers this week to look forward to, if anything the sun will be a welcome return!

Edited February 7, 2010 by mark bayley

[nick sussex]

That is probably the biggest risk as the -NAO converts more to a west base. This chart suggests that we are perfectly positioned in the UK before that occurs:

Preferably we'd like to see the models edge the pattern eastwards with time, i don't doubt theres the possibility for some major snow but its whether the Scandi trough will back too far west after this.

[PubliusEnigma]

Here's the 850hpa temps for that period

Turning milder in the far south, colder from the midlands North. I wouldn't worry to much at this stage. There will be many evolutions over the coming days. I remember GP saying a west based NAO was likely, which then opened the risk of attack from the South West. We shall just have to watch the models over the coming days. The high retrogressing north westwards seems very likely after the initial easterly.

This is my concern that we are could be 9 days away from the breakdown to mild, with a possible sleet to rain transient

affair for the South , possibly with quite a bit of snow on the leading edge for the midlands northwards, if the low

is further west, there could be a greater mild insurgency.

[Jason T]

It will be very interesting to see what the models will be like this time next week, I know most really stick to no more than +96h as this is with in comfort zone, but that ecm at+240h on meteociel is a corker. I know thats 10 days away and lots can change in that time frame but will be interesting to see what happens.

Edited February 7, 2010 by silver line

[January Snowstorm]

I

We have reached the time of year when a thin snow cover tends to melt in the sun even with low temperatures because as soon as a hole is punched in the snow cover, especially over concrete surfaces, the sun heats up the surface and accelerates the thaw in surrounding areas. But a reasonably thick snow cover tends to reflect solar radiation making the sun less of an issue.

Your forgetting one important point tws

Ground Temps!, are remarkably low after such a cold January. This will surely help against much thawing

[gottolovethisweather]

Hello,

Posting again in order to stop the confusion.

While many folk on here, especially lurkers (normally including myself) are contemplating the pub run of the GFS and what it has to offer up to 16 days out, I suggest they/you take on board some of the last few comments on the cold discussion , which I feel are very appropriate indeed.

Whoops I meant the MODEL MOODS THREAD, apologies IMO it still applies though to our model output obsession.

I'm very much liking the GFS out to T+72, oh yes.

STORMBOY

Edited February 7, 2010 by STORMBOY

[Filski]

Feb 2009 saw sheet ice hanging around for days in London. Not as long as Jan admittedly but still a decent prospect if a couple of inches can settle.

[lorenzo]

After GP post I found this GFS Ensembles Loop which shows the progression into next weekend quite well.

http://www.meteo.psu.edu/~gadomski/ENSHGTAVGNH_12z/ensloopmref.html

Edited February 7, 2010 by lorenzo

[Jan 87]

extended ecm ens do indicate the block going too far west and us ending up on the wrong side of the jet.

[Tim Bland]

extended ecm ens do indicate the block going too far west and us ending up on the wrong side of the jet.

We should wait for the London ensembles before jumping to conclusions. A Northerly would bring milder air to Holland but not necessarily us!

[ITSY]

extended ecm ens do indicate the block going too far west and us ending up on the wrong side of the jet.

PATIENCE grasshoper. Patience.

And in answer to the question made earlier by a poster; unfortunately, it won't be a US East Coast snowpocalypse. We could have the heaviest snowfall to lower levels for 50 years and it still wouldn't be.

That doesn't go to say that we should rule out any kind of snowfall. In my opinion, by the time we get to the end of the week, heavy showers COULD crop up almost anywhere - going off of recent model runs; BEEBBC and Metoffice forecasts and opinions on here and on TWO.

remember that even the Metofficet mention the prospect of significant snowfall on their 3-5 day forecast.

Nothing is off the cards yet; unless, that is, you're after 41-91cms.

[gottolovethisweather]

Oh well.

Hello,

Posting again in order to stop the confusion.

While many folk on here, especially lurkers (normally including myself) are contemplating the pub run of the GFS and what it has to offer up to 16 days out, I suggest they/you take on board some of the last few comments on the cold discussion , which I feel are very appropriate indeed.

Whoops I meant the MODEL MOODS THREAD, apologies IMO it still applies though to our model output obsession.

I'm very much liking the GFS out to T+72, oh yes.

STORMBOY

[ITSY]

Perhaps the chance of some snow into wedneday night? As predicted by the Metoffice? A colder run so far? -4C down the central spine of England during/on Wednesday night

[SMU]

disclaimer its the 18z,however better angle of flow from the east at day 4 & that looks lke a shortwave in the north sea to help swing things further-

http://91.121.94.83/modeles/gfs/run/gfsnh-0-96.png?18

I expect the ensemble mean to reach -12c for the SE by tomorrow morning,I dont think the 12z was very reflective of whats going to happen-

S

[Lewis]

disclaimer its the 18z,however better angle of flow from the east at day 4 & that looks lke a shortwave in the north sea to help swing things further-

http://91.121.94.83/modeles/gfs/run/gfsnh-0-96.png?18

I expect the ensemble mean to reach -12c for the SE by tomorrow morning,I dont think the 12z was very reflective of whats going to happen-

S

Hi steve, you beat me to it!

I must say, the way this runs panning out, the high just gets pushed back further NW, during wednesday night into thursday the easterly trys to push in, succeeds down south, kind of fails with me just staying on the SE most edge of the HP, then within a few hour it gets shunted away and the flood gates open, mean for the SE -12, with the mean i would say -11 for me, i would not be surprised if these 850 pools get colder!

Lovely run, truely lovely.

Edited February 7, 2010 by Storm Force Lewis

[cooling climate]

I think thawing during the daytime is very likely early in the week with maximum temperatures between 3 and 5C- this will tend to cause some thawing of snow cover regardless of how much sunshine there is, especially as very few places can expect much snow on the ground to begin with. Towards the back end of the week, if this easterly comes off, we should see maximum temperatures near freezing and a more widespread/significant snow cover which should make it far more resistant to thawing in sunshine.

We have reached the time of year when a thin snow cover tends to melt in the sun even with low temperatures because as soon as a hole is punched in the snow cover, especially over concrete surfaces, the sun heats up the surface and accelerates the thaw in surrounding areas. But a reasonably thick snow cover tends to reflect solar radiation making the sun less of an issue.

Yes, it is probably stating the obvious but with temperatures above 0c during the day there

will be thawing of any lying snow whether it be January or in this case February. To combat a

slightly stronger sun compared to January the temperatures need to be at freezing to +1c at

best to ensure a good snowpack.

A better 18z operational than the 12z I see with it slightly more in line with the Euro models.

[cold snap]

Excelent 18Z

The evolution is so slow.which is a pity

Moderators going to be overworked this week.if this model patern stays as it is.

People try not to become inpatient.

I know its hard.rewards look good towards the end of the week says ECM.UKMO.GFS

[karyo]

A good 18z with more snow showers around than the 12z and also yesterday's 18z! Some snow showers look likely too cross the Pennines from time to time.

Karyo