Model Output Discussion: 12Z (20/11/12) And On...

[Downburst]

Around 200h WE see a low moving up from the south... Interesting not on this run but if it did happen then i'm sure it would be modeled much further south due to the block so lots of snow for the south! Seen this happen a few times when the models underestimate the blocking

Yes indeed, usually happens that a low comes from the south or south west and a "battle ground" happens at the end of all easterlies. the undercut is very common and usually produces the most snow in volume terms, the snow might not last very long as the cold snap ends post this. But hey we all know that it can't last.

[SMU]

wow

I was looking at the angle of the shortwave off NW russia at 96 on the GFS at 96 then had another window open for the Control-

I would say be have the most identical match in history at T96- which is no mean mean feat-

open these 2 for the NH- then tab between each other-

http://modeles.meteociel.fr/modeles/gfs/runs/2012112118/gfsnh-0-90.png?18 OP

http://modeles.meteociel.fr/modeles/gens/run/gensnh-0-1-90.png?18 Control

SOLID.

[Bristawl Si]

Re. the blizzard showing in northern England in the GFS FI, it would probably only be significant on high ground- a marginal rain/sleet event would be more likely at low levels due to the lack of a strong push of cold air from the Arctic- though it's unlikely to come off as shown in any case. The north-easterly incursion showing at the end of the ECMWF operational run has a distinctly snowy look to it, while the ensemble mean continues to suggest a cold (though not remarkably so) and showery north-easterly type from T+144 out to T+240. A snowy start to December is looking increasingly probable on the basis of today's model runs, though at this range there is still plenty of scope for change either way.

Before that, we have to watch out for a vicious low pressure system over the weekend which has been steadily toned up by the models over the past few runs. The ECMWF shows a strong low with strong to gale force winds and heavy rain- this could well cause real problems for the areas that are currently on flood alerts, in addition to tomorrow's rain belt- but the GFS and UKMO have a much shallower version, with the GFS version just producing some light-moderate rain over the south, so this one is worth keeping a close eye on.

7

TWS- Ian F was hinting at poss snow event on N/NW flank Sat night - not major but a possibility - any thoughts?

Edited November 21, 2012 by Bristle boy

[Downburst]

When is the first, I am afraid to say this is a terrible run, not as cold as 1963, or 1947 or 1979 etc etc. going to come. Then 18 year olds will be smacking their heads off the table, "not as cold as 1963 dammit" posts? It's amazing to even flirt with this in November. Even if it doesn't snow it will be amazing to have a biting easterly and most normal people will get that.

[Weathizard]

The 18z looks a decent run on the face of it, the sypnotics are fantastic here and if all pieces fall into place, if we get that bit of luck, this is the sort of time where records can be broken, I have never seen charts with such good sypnotics, hopefully it all falls into place. Personally can't see the low at 144ish developing like that and far too often we see the GFS over-cooking the effect of low pressure systems

[Duane S.]

GFS D7 H5 anomalies says it all really- the hotspot being E Greenland- which is the pinnacle for the H5 +ve anomalies- and it stretches through the Arctic- all the way to the Aleutians! Major trough activity o/ France and the continent- one hell of a chart

How anybody could find fault with this week's output is beyond me (other than nitpicking for the sake of it) and this outrageous anomaly chart just highlights it even more graphically.

Same old caveats apply but we are in for one heck of a start to December!

18z another theme on the evolving pattern and that theme will chop and change for many days yet,for the good and the bad but I just can't see now how we are not going to get a decent cold snap a the very minimum. We need to make sure as much energy goes into the southern arm of the jet, certainly seems to be perfectly plausable

+ Steve's 1933 chart. Very tasty!

[Pixel]

even to my untrained eye it looks like the north pole has moved on this pub run - you couldn't make it up

definition of fantasy Island (FI) surely (-:

[kold weather]

Well the GFS ensembles are showing why I thought the GFS run was risky, some runs just sim,ply don't eject that trough at all and it sticks and we end up with very little actual deep cold around Europe despite great synoptics.

We want that low to eject ESE as FAST as possible, the longer it waits around, the longer it takes to get our cold feed. We got away with it on the 18z run because the blockin was so strong, but on other ensemble members we aren't so lucky.

[weather eater]

Ring any bells

[phil nw.]

What an upbeat day for all cold lovers!

The good thing now is the pattern change is within the more reliable time frame with the Atlantic high ridging towards Greenland and the trough over the UK disrupting between 96-120hrs.

Great stuff and good to see all those background signals we have been following bearing fruit.

[Downburst]

The very warm sea surface temp anomaly south of Greenland and the counter clockwise move of air in the NH and the very big surface HP anomaly to the east of the HP. Is there a link I wonder. I know GP can answer but I would love to hear simply put what is causing this.

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

Pick of the ensembles for early cold!

[kold weather]

Control run is pretty tasty at 216hrs, looks ALOT like the 12z ECM except we have any big plume going up in the Atlantic...thats superb to see for long term chances.

http://modeles.meteociel.fr/modeles/gens/run/gens-0-1-216.png?18

If we get a second bite of the cherry, that will be the proper cold one, this one is really setting the scene IMO, helping to cool Europe down and to get those SST's in the North Sea a little lower.

[ukpaul]

Ensembles trending colder and colder, a third or more with high snow potential for the south (more for the North I would imagine) by next Friday onwards. Not bad for a setup that they often find difficult to pin down at that range.

[BlueHedgehog074]

With over 20 pages worth of model discussion today, it's clear the various charts are producing the 'dream' the cold/snow/frosty fans are after.

Fingers crossed the models don't do a sudden change tomorrow and break our hearts (although with good model agreement with blocking to the West/North-West/North and a cool/cold airflow generally between the North and East, I feel confident our hearts won't be broken). It's clear the placement of the Low Pressure systems to the South-East/East will make the difference in how deep the cold gets and how likely wintry weather becomes.

I agree it's been quite an enjoyable day for chart-watching overall.

Edited November 21, 2012 by DiagonalRedLine

[crimsonp]

i've been keeping an eye on the models pretty much all day and sure the 12z caused some fuss and excitement among those, like me, who live on fi but all i can say about the 18z fi is GREAT HOLY MACGOALY!!!!!

stewart's preliminary winter thoughts look pretty much verified!! hope the festive run comes up trumps too..... fingers crossed!!

the morning run seems an age away now.... like the one last sleep before crimbo...........

Edited November 21, 2012 by crimsonp

[nick sussex]

Well the GFS ensembles are showing why I thought the GFS run was risky, some runs just sim,ply don't eject that trough at all and it sticks and we end up with very little actual deep cold around Europe despite great synoptics.

We want that low to eject ESE as FAST as possible, the longer it waits around, the longer it takes to get our cold feed. We got away with it on the 18z run because the blockin was so strong, but on other ensemble members we aren't so lucky.

Thats a good point KW.

This troughing could become slow moving and so its preferable to get this se of the UK, especially in case it deepens.

You'd think though given the strength of the ridge to the north it should place enough forcing to eventually shift it. Of course though better to have that higher margin for error.

[Mark Neal.]

What a fantastic day of model watching. Coming home from work this evening and having to trawl through 5/6 pages of unread posts was very amusing. Some amazing charts and even the chance of snow being shown too. I remember saying a few weeks back i would love to see snow this side of xmas, may just get that!

Edited November 21, 2012 by Mark Neal.

[Thundery wintry showers]

7

TWS- Ian F was hinting at poss snow event on N/NW flank Sat night - not major but a possibility - any thoughts?

I've had a look at the model outputs and I think there's a possibility on high ground if the low ends up quite deep and northerly tracking as per the ECMWF, but I think low-lying areas are unlikely to get snow from it. It's pretty hard to call at the moment though because of how much disagreement there is between the models despite it being just four days away.

Edited November 22, 2012 by Thundery wintry showers

[Met4Cast]

Ensemble mean trending colder still on the 18z, OP run appears to be an outlier

[cyclonic happiness]

Ensemble mean trending colder still on the 18z, OP run appears to be an outlier

Very good news Dan, I think there's time for more upgrades as we iron out the creases.

I said last week that I thought the GFS was onto something because it was having one of it's characteristic 'wobbles' that only seem to appear before major cold spells.

Will the polar vortex be shoved over Britain, at the rate the northern blocking was expanding, there doesn't seem like there's anything else it can do :-P

[summer blizzard]

It seems that the reason the GFS18z gets away with stalling the low but getting the cold air is that it makes very little of what was forecast to be a low bombing from the south west and as such little mild air is dragged up with it. At this stage i would have to assume this run to be an outlier in that regard however it is possible that the models could drop it.

Great to see the ensembles are very much on board now and that sufficiently cold air will be arriving on day 7-9.

On a lighter note those wanting to see a true blizzard should go to southern Scandinavia in about a week..

[Fozfoster]

Going to sleep happy good night all!!

[Duane S.]

It does seem at the moment, as we head towards the details window in a few days time, that one possible area for mad members' moods swings will indeed be the trough ejected down through us.

As always in these type of situations we want to see it pass as quick as possible down through us, with every mb decrease in pressure will increase its tendancy to not want to do so though, so we don't want to see it deepening too much. So, it may be it doesn't sink initially as much as us southerners at least would like to see it, but you'd have to say that blocking from above and the jetstream slipping further south may prove this a southern spoiler only for a couple of days before the wintery stuff arrives down here as well. Just some thoughts.

[kumquat]

As my old gran used to say:

"When the 528 dam starts skirting the Mid Atlantic Ridge

It's time for the UK to go into the fridge....."

Tada

It seems that the reason the GFS18z gets away with stalling the low but getting the cold air is that it makes very little of what was forecast to be a low bombing from the south west and as such little mild air is dragged up with it. At this stage i would have to assume this run to be an outlier in that regard however it is possible that the models could drop it.

Great to see the ensembles are very much on board now and that sufficiently cold air will be arriving on day 7-9.

On a lighter note those wanting to see a true blizzard should go to southern Scandinavia in about a week..