General Model Output Discussion

[snowmadchrisuk]

what's your forecast for Leicester chris? Up here at my mums for Christmas so fancy some snow. We seem to be right at the margin in terms of ppn and cold air.

Touch and go IMO the Met Office say Higher Parts of Leicester. That's if the ppn even get's this far , although the GFS says it will.

I think where you are you could get rain , but if it is Snow it will be very heavy Wet Snow ... The map I posted earlier from the NEA model gives a good idea what all the tv forecasts are thinking right now.

[West is Best]

When we had the heaviest snowfall for 20 years in north Devon this February ALL the models progged everything too far north and too far east. The whole lot stalled further west and south.

Watch this: stalling low being pushed back by the increasingly potent easterly. I firmly predict the incursion will be LESS far north and east, as happened in February. I think ECM/GEM/FAX are going to prove closest to the mark here.

Ian - cold night last night. The cold is digging in at just the right time ahead of the front. And it's the fact that the easterly picks up, pulling in really cold uppers that increases the snowfall potential hugely.

[Cymro]

When we had the heaviest snowfall for 20 years in north Devon this February ALL the models progged everything too far north and too far east. The whole lot stalled further west and south.

Watch this: stalling low being pushed back by the increasingly potent easterly. I firmly predict the incursion will be LESS far north and east, as happened in February. I think ECM/GEM/FAX are going to prove closest to the mark here.

Ian - cold night last night. The cold is digging in at just the right time ahead of the front. And it's the fact that the easterly picks up, pulling in really cold uppers that increases the snowfall potential hugely.

Yes but I personally don't feel that the cold over the Uk is potent enough to stall the precipitation as much as forecasters are suggesting.

[Duane S.]

Personally I think we have seen the models prog this as far North as any of them will from now on in. The only way the Northerly edge of this is likely to go now is further South.

Despite Ian Brown stating just one hour ago that it would be, and I quote, "obviously a big disappointment for Wales and the Midlands" this is the area that looks most likely to be hit. But... as some others have alluded to I could quite see areas further south, and unfortunately I doubt that includes me, getting a surprisly big snowfall from this. I'm thinking Somerset/North Dorset through to North Kent potentially.

[Altostratus]

The ECM hasn’t budged and the latest GFS has shifted the low further south. I know which model I would back in this situation. I expect the GFS will slowly come around to the idea in subsequent runs.

The BBC must be reasonably confident as it quite uncharacteristic of them talking about snow distribution a few days out. I remember in Feb 2001 John Kettley and everyone else, bar the UKMet and BBC, were forecasting severe cold and snow for the entire UK. The BBC were adamant that the coldest air wouldn't reach the majority of the UK. Guess who was right that time?

[Guest North Sea Snow Convection]

Putting aside the 'is it north or is it south' and 'will it snow and where' issue debate within the 'Cyclogate' saga - the ECM and GEM continue to be solidly consistent both in how they handle this silly boring low, and how it evolves into an easterly. I have to be honest that I am not even bothering to look at the GFS atm, as the pattern through to the weekend is cleared up now. And that is also notwithstanding the UKMO which has gone off on one this morning too.

The most important thing as far as I am concerned is what happens after the 'post low' period.

[Pennine Ten Foot Drifts]

I'm finding this all extremely difficult to understand to be honest. Taking GFS 06Z at only T42, (what I believe used to be termed 'nailed' !!!), 850s, DPs, and temps would all categorically point to rain for everywhere south of somewhere between the M62 and the A66 (depending to a certain extent on elevation of course), and certainly for the whole of Southern Britain, with 850s of 0-5C, DPs of 3-7C and surface temps of 1-6C it ain't gonna be snow !. So how can it be this wrong at such a short timescale (i.e. precipitation 100+ miles out, 850s 5C+ out, DPs 5C+ out)?

[Mondy]

Yes but I personally don't feel that the cold over the Uk is potent enough to stall the precipitation as much as forecasters are suggesting.

I can assure you it's potent enough already up here - just look at any decent temp chart and you'll see.

[Duane S.]

The most important thing as far as I am concerned is what happens after the 'post low' period.

I totally agree with that but of course it is still important to see that low behave itself as its track will have a big impact on the post-low setup.

[Cymro]

I can assure you it's potent enough already up here - just look at any decent temp chart and you'll see.

Oh I know it is in Scotland I mean in the Uk as a whole. Got down to -5 here last night but its been one day here ater the brief mild interlude therfore I'm not too sure.

[Guest North Sea Snow Convection]

I totally agree with that but of course it is still important to see that low behave itself as its track will have a big impact on the post-low setup.

That was important yes - but as far as I can see (and I am deliberately ignoring the GFS for this reason) the post low set-up now looks pretty good irrespective of the margins of rain/snow over the UK over the middle part of this week.

Edited December 28, 2009 by North Sea Snow Convection

[If Wishes made Weather]

A subtly different GFS run:

The 00z showed a low pressure system developing over Russia. This had the effect of channelling colder air down into the Black Sea region. The 06 z does not develop this feature (which of itself is interesting in terms of model consistency in the high res early part of the run) and accordingly, western Europe sees a better direct feed of air from Russia. Pressure is then (accordingly) shown as higher over the near continent than in the 00z run.

Otherwise

1 low runs straight up the channel

2 it is more circular in form rather than oval

3 – accordingly the SE sees higher upper temps for longer with the -5 line running on the 850 charts from Bristol to Hull.

4 – the upper milder segment in the low is more pronounced and held intact for longer.

5 – there is no further low modelled in the south west approaches as the 00z had at T 141

My impression is that whereas we are clearly not in a typical westerly weather fed winter, the signals/elements for a strong feed from the east are not quite there, but are showing increasingly strongly in all models as time progresses.

[swilliam]

I'm finding this all extremely difficult to understand to be honest. Taking GFS 06Z at only T42, (what I believe used to be termed 'nailed' !!!), 850s, DPs, and temps would all categorically point to rain for everywhere south of somewhere between the M62 and the A66 (depending to a certain extent on elevation of course), and certainly for the whole of Southern Britain, with 850s of 0-5C, DPs of 3-7C and surface temps of 1-6C it ain't gonna be snow !. So how can it be this wrong at such a short timescale (i.e. precipitation 100+ miles out, 850s 5C+ out, DPs 5C+ out)?

Because it is a numerical model!

As for the beeb back tracking they have consistently said that there is a lot of uncertainty at the moment- what else do you want. They are going with their high res models and other information and calling it as they see it at the moment. They also can see the discrepancies in the low res models and are allowing for that.

[SMU]

http://91.121.94.83/modeles/gfs/run/gfsnh-0-168.png?6

PERFECT Chart for me...

PS not sure where people are getting the southward movement-- must be imagination-

Go to the meteociel Archive & the 00z PPN belt is in exactly the same place at 42 as the 06z is at 36, the same replicates at 78 V 72-

If your in the south forget it & hope for the end of the week - epecially hope that the trough gets far enough SE to allow the intial cold easterly in at around 96-

For those in the risk zone I mentioned yesterday, all the southern counties are probably out of the question with a shift northwards of ~75/100 miles-

It will be interesting what North wales gets still-

S

Edited December 28, 2009 by Steve Murr

[swfc]

So once this"now boring low episode"is out of the way how do we think it will pan out regarding shower activity and temps.Difficult to forecast but the outlook does like staying cold with plenty of blocking here there and everywhere.

[80sWeather]

+T168 Could the GFS be lining up another attack from the south,mind though i dont know what to believe now,this is the best rollercoaster ride the models have ever taken us on.

[TEITS]

So how can it be this wrong at such a short timescale (i.e. precipitation 100+ miles out, 850s 5C+ out, DPs 5C+ out)?

Like I said earlier remember just before xmas how Luton airport was closed and how some had to abandon their cars due to the heavy snow. Well at 4am on that very day the GFS predicted a lovely sunny, dry day. However the Met O/Fax suggested snowfall.

However in saying this even I think the Fax charts probably have the fronts too far S. Im going for something inbetween the Fax/GFS. You often find with disagreement the answer lies inbetween.

Just add that I have to laugh at the difference between the 0Z/06Z in the medium range. For this period I am definately sticking with the ECM/GEM.

Edited December 28, 2009 by THE EYE IN THE SKY

[Paul]

Can I just remind everyone that this is the model discussion thread, we do have a general cold spell chat thread here for non model related discussion:

[Weather-history]

I'm finding this all extremely difficult to understand to be honest. Taking GFS 06Z at only T42, (what I believe used to be termed 'nailed' !!!), 850s, DPs, and temps would all categorically point to rain for everywhere south of somewhere between the M62 and the A66 (depending to a certain extent on elevation of course), and certainly for the whole of Southern Britain, with 850s of 0-5C, DPs of 3-7C and surface temps of 1-6C it ain't gonna be snow !. So how can it be this wrong at such a short timescale (i.e. precipitation 100+ miles out, 850s 5C+ out, DPs 5C+ out)?

So how can UKMO Fax charts be so wrong at this range?

Its far too easy to say that can't be wrong because you need to explain why the other side is so wrong then.

Edited December 28, 2009 by Mr_Data

[kold weather]

ECM model now on its own with regards to how it evolves this pattern, looks like the 18z saw a good trend in that respect.

Anyway the 06z is still way too progressive with the dropping of the -ve NAO, reducing heights as early as 168hrs which I think is going to end up at least 3-5 days too quick, as we saw with the last cold spell which took 4-5 days longer to break down then the first wave of forecasts for it projected...expect this cold spell to get lengthened more akin to the 0z GFS and the 0z ECM...not the lala land of the 06z...

Looks like being a painfully slow evolution to cold for the SE as the LP anchors in...this could however mean good stuff for places NW becuase by that time colder air would be filtering in around the low.

[Guest North Sea Snow Convection]

So once this"now boring low episode"is out of the way how do we think it will pan out regarding shower activity and temps.Difficult to forecast but the outlook does like staying cold with plenty of blocking here there and everywhere.

I'm sure that the snow region in terms of this low - some central areas, are excited and delighted with prospects this week. And very rightly so But I think that for the model thread it might clutter up with too much discussion in terms of who gets snow where - in terms of this low - that's all I mean. Also I was suggesting that the GFS is wasting a lot of nervous energy on people in terms of its jumpy output - so in that respect, at least imo, a better and more consistent guide might be taken from the ECM and GEM which I think clearly are handling this overall pattern much better. Also it looks to me as if the METO.BBC,NOAA and other professional agencies are using the guidance of these models as well. Says it all to me really.

The whole UK is looking at the t96 period in terms of fortunes of what happens following the low - particular interest is the progress of some REAL cold air out to the north east. The model trend has been, and still is, trending quite promisingly in terms of advecting this closer to the UK, much as I for one was suggesting yesterday There would be no marginality and much less uncertainty involved with that airstream over the UK, that is for sure!

Edited December 28, 2009 by North Sea Snow Convection

[J10]

The NAE model which last night pushed north has now pushed back south (by around half last nights edge north), and these forecasts are pretty much in line with what we see on the TV.

It also has the low pressure further south than the UKMO.

[Tucco]

A number of the 06z runs have the precip further North well into Scotland than the op.

No backing down from 06z

http://91.121.94.83/modeles/gens/run/gens-1-0-48.png?6

http://91.121.94.83/modeles/gens/run/gens-3-0-48.png?6

http://91.121.94.83/modeles/gens/run/gens-4-0-48.png?6

http://91.121.94.83/modeles/gens/run/gens-5-0-48.png?6

http://91.121.94.83/modeles/gens/run/gens-6-0-48.png?6

http://91.121.94.83/modeles/gens/run/gens-7-0-48.png?6 Further South

http://91.121.94.83/modeles/gens/run/gens-8-0-48.png?6

http://91.121.94.83/modeles/gens/run/gens-9-0-48.png?6

Well you get the idea

Mark

Teesdale

[Guest North Sea Snow Convection]

ECM model now on its own with regards to how it evolves this pattern, looks like the 18z saw a good trend in that respect.

Anyway the 06z is still way too progressive with the dropping of the -ve NAO, reducing heights as early as 168hrs which I think is going to end up at least 3-5 days too quick, as we saw with the last cold spell which took 4-5 days longer to break down then the first wave of forecasts for it projected...expect this cold spell to get lengthened more akin to the 0z GFS and the 0z ECM...not the lala land of the 06z...

Looks like being a painfully slow evolution to cold for the SE as the LP anchors in...this could however mean good stuff for places NW becuase by that time colder air would be filtering in around the low.

Not sure how that is the case? As you go on to suggest, the GFS is too progressive in terms of what it does with the pattern. The way I see it, the ECM and GEM have lead the pattern and the GFS has over complicated and jumped around behind.

[kold weather]

Whats really interesting is we still evolve into a cold spell on the ECM/GFS but in very different methods. On the ECM the low is far enough south to drag in an easterly flow anyway however the core of the Greenland high remains in place. Meanwhile the 06z op slowly drags the whole thing SE which forces an easterly flow of some sorts...

I suspect the GFS will be closer to the mark BUT importantly that high won't come down anywhere nearly as quickly as the GFS is wanting it to...it could do but I think its rather the outside chance rather then the most likely option.