Model Output Discussion

[Duane S.]

Many saying they have never seen charts projected like this before so close ... I'm sure I have seen charts projected like this a few or more times over the years at similar timeframes - just that the promise has either gone pear-shaped or ended-up much less cold and snowy than progged, so worth bearing in mind.

However, haven't seen the models be this consistent over consecutive runs this far out with a blocked and cold pattern ahead with no real threat to break it ... so we could be on the verge of something special that we haven't experienced for a while - i.e. a protracted cold and potentially snowy spell.

Absolutely. The consistency of the charts leading up to this cold spell has been like nothing I can remember. It's this more than anything that leads me to think it will occur (in one fashion or another)

[Snowaddict]

Stunning set of 18z ensembles, even at T+120 with the HP cell cut off to our immediate north, ridging Northwest.

First set of ensembles on which the mean also reaches -8 in Dublin, indicating increasing continuity for the westward progression of deep cold air...

It's hard to believe what we are seeing really as if this verifies, many parts of the country could well experience significant disruption...

[kold weather]

The control shows a less good set-up where the shortwave goes over the UK then loses itself so to speak which means the cold air doesn't tuck in as well and takes longer.

FWIW though there will be a decent set-up still from it...

[Iceni]

Last frame of the parallel-

SNOWIEST Christmas EVER?!

http://91.121.94.83/...fs-0-384.png?18

SW would be buried in the stuff.

I have a 'Good charts' folder and that one has just gone in with knobs on.

I also placed a bet of £20 for a white Christmas today odds 4-1, down from 7-1 last night so something may be afoot. I can't believe temperatures will zoom up to 7C after a week or so of lying (we hope) snow at this time of year with just 8 1/2 hours of daylight. :cold:

[weather eater]

I thought the 18z was pretty bonkers and the parallel, even more so. Yet again I have to say the consistency from the parallel is outstanding. On the subject that has been raised in terms of snowfall being put back, I feel much nonsense is being talked about in this regard. Sunday/Monday cold air gets into the south east, a milder (if we can call it that) interlude for Tuesday, then the cold air digs back down. Of course with this the best part of a week away much can change, but for me it’s getting the blocks in place over the next four days, if that happens OK then I'm sure all of us will feel the cold and I'm pretty certain that a extended spell with plenty of the white stuff will be on offer for a great many, even if the models haven’t got it exactly right yet.

[Polar Side]

Evening guys, some of these charts are incredible.

Can any of the experts tell me when or how often in the past have we been on the south east side of an omega block (in winter) ?

Also, someone posted earlier about seeing the elusive dendrite snow flakes falling. I take it this would be possible if we tap into the really cold uppers later next week ?

[cyclonic happiness]

If this lot verfies going by the parra run, then the word "marginal" will be a term of the past.

even Sunday/Monday isn't beyond the realms of certainty.

[TEITS]

The whole setups marginal Eye. The NErly 144hrs+ is better suited for higher ground Scotland and NE England. With the low tracking so close to the SE the warm sector within the low would do nothing more then aid in stirring the mild air across the NE sea.

I'd say the easterly is likely to give a better ratio to rain snow then the NE'ly. But that's what I'm seeing.

Lets have a look at +180.

http://www.wetterzentrale.de/pics/Rmgfs1802.gif

http://www.wetterzentrale.de/pics/Rmgfs1808.gif

So upper temps between -10/-12C with DP as low as -7C. The max temps on this day are likely to be around 0C or even -1C.

Now consider this the feb 09 snowfall you see on my sig occured with upper temps of -4C, DP 0C, max temp 0C. Are you honestly suggesting those +180 charts would be marginal!

[LomondSnowstorm]

Ensemble mean has again kept the cold spell coming for late Tuesday/Wednesday:

[Jan_Bromley]

Whilst we need a trigger to bring the coldest air in from the arctic across Scandi (Copenhagen) and all routes SW of there, it needs, yes, to be a feature that is significant enough to advect the arctic continental airflow right through the UK but not so over-developed that it becomes like a cyclonic frontal system that takes energy from the 'tropical' side of the system and then sets up a barrier zone to the cold air as it tries to move south and in turn forms a dynamic whereby it stops moving south and halts the progress of the cold air. If you see what my simple mind is trying to say!?

It is very early days, but there is just the hint in my mind that this sort of process as described is being sown and that this north sea low is going to become a more and more significant player (and spoiling nuisance for southern parts of the UK). The time period to get the colder air is not coming nearer, the advecton of cold period should be this weekend for a decisive countrywide event and that may be significant in terms of the extent of this very potent arctic outbreak.

But I think that we will find that the favoured areas will end up being NE parts of the UK (who could see some quite severe conditions)as the path of the low tracks less further south but further west from the north sea into central parts of the UK as the modelling progresses over the next day or so. It could be that SE parts in particular end up on the warm side of the low with a returning flow from the channel (ie a south westerly wind) as the low links up with the advancing southerly tracking troughs in the SW approaches.

That is exactly my worry. Living in bromley as I do, Iam concerned that it will marginally be just too warm, ending up with cold sludge instead.

[Tom Montalbano]

We seem to be getting quite a bit of cross model agreement now at around t168/t192, albeit a fair way off still. Low moving down N.Sea to be close to the Dutch/Danish coast, ideally we would want this to track a little further south.

http://charts.netweather.tv/gfsimages/gfs.20091209/18/177/h500slp.png

http://212.100.247.145/ecmimages/20091209/12/ecm500.192.png

http://www.wetterzentrale.de/pics/Rjma1681.gif (A smaller feature, granted).

http://www.wetterzentrale.de/pics/Rukm1441.gif (Possible if it went out to 168/192, would show similar)

Regards,

Tom

[kold weather]

As for events closer to the here and now, the set-up on Sunday looks a little on the wrong side of marginal, in the overnight hours though it could turn a little wintry I suppose. Monday eveing would be better but once again this is all marginal stuff and most of the time will be on the wrong side of marginal upto 168hrs, where obviously if we get a proper NE flow then things go the right side of marginal.

[Optimus Prime]

Lets have a look at +180.

http://www.wetterzentrale.de/pics/Rmgfs1802.gif

http://www.wetterzentrale.de/pics/Rmgfs1808.gif

So upper temps between -10/-12C with DP as low as -7C. The max temps on this day are likely to be around 0C or even -1C.

Now consider this the feb 09 snowfall you see on my sig occured with upper temps of -4C, DP 0C, max temp 0C. Are you honestly suggesting those +180 charts would be marginal!

Lets just clarify the second chart isn't 2M temperature it is dew points (I know you already stated that but you know what some people are like)

Firstly the first chart you posted is before the precip moves in, look at the higher 1500m temperatures around the low and also take into account the high surface temperatures being dragged in from the abnormally warm seas. The NE and higher ground would do well but where you and me live at around sea level it would be a wintrymix.

Secondly the easterly in Feb has -15 1500M temperature move across us with -12c more generally. Even so it was still somewhat marginal as I remember the temperature being around -0.6c at the time of the falling snow. And that was a direct Easterly of the frozen continent (Englands COLDEST source)

Come on Eye look at this objectively.

PS- I'm in total agreement with North Sea Snow Convection. That's my exact thought.

Kold - Easterly is colder then a NErly. The upcoming NEy may actually be colder but only because the precip will be in the continuous form rather then sporadic/showery.

Edited December 9, 2009 by Optimus Prime

[Cecil Hogmanay Melchett]

One more day and the block to the NW will be nailed on.These are THE dream synoptics we are seeing-

Greenland/Icelandic block-

PV dropping into Scandanavia-

Pressure falling right across Southern Europe-

Now,if if if this does verify its something ive personally been waiting for for years.We will be into the

2nd half of Dec which means short days and a very weak sun.Today the sun set here at about 3.30pm,i watched it!

I know some will disagree but these synoptics are better in the 2nd half of Dec than mid to late Feb,if the

uppers are cold enough the sea will be our friend,potential for some big instabilty in the flow and i inc polar lows

in that process.

[cooling climate]

Do we all agree while being an exceptional setup for the time of year what the GFS is showing this isn't a 1981 and it won't bring us countrywide snowstorms ala Dec 62/78/81? And temperatures won't be that cold.

There is very good reason to believe that it could be colder and snowier than 81.

The models are showing us that.I can not understand the despondency from some quarters.

We have been waiting years for synoptics like this, these charts should be savored and

enjoyed heck we have been waiting long enough.

Personally I think it will be colder than what some of the model runs are showing we

shall see.

[timistry]

Stunning set of 18z ensembles, even at T+120 with the HP cell cut off to our immediate north, ridging Northwest.

First set of ensembles on which the mean also reaches -8 in Dublin, indicating increasing continuity for the westward progression of deep cold air...

It's hard to believe what we are seeing really as if this verifies, many parts of the country could well experience significant disruption...

About 100miles further west will do nicely. Then maybe a low nudging up against a NE'ly flow creating a battleground situation

[Duane S.]

One more day and the block to the NW will be nailed on.These are THE dream synoptics we are seeing-

Greenland/Icelandic block-

PV dropping into Scandanavia-

Pressure falling right across Southern Europe-

Now,if if if this does verify its something ive personally been waiting for for years.We will be into the

2nd half of Dec which means short days and a very weak sun.Today the sun set here at about 3.30pm,i watched it!

I know some will disagree but these synoptics are better in the 2nd half of Dec than mid to late Feb,if the

uppers are cold enough the sea will be our friend,potential for some big instabilty in the flow and i inc polar lows

in that process.

I think that part is already nailed on. Too many signals for that part now not to happen IMO. It's what happens next that is understandably up in the air!

Not a bad position to be in though as you say!

[TEITS]

Secondly the easterly in Feb has -15 1500M temperature move across us with -12c more generally. Even so it was still somewhat marginal as I remember the temperature being around -0.6c at the time of the falling snow. And that was a direct Easterly of the frozen continent (Englands COLDEST source)

Come on Eye look at this objectively.

The snowfall in feb that im referring to didn't occur during the E,ly with those cold upper temps. The only snowfall that fell during that Sunday evening was the thames streamer that affected parts of london.

Here is the period im referring to and if you bothered to look at my sig you will note the 5th Feb!

http://www.wetterzentrale.de/archive/ra/2009/Rrea00220090205.gif

Come on OP look at this objectively!

Edit I can't see mucn green on this chart.

http://charts.netweather.tv/gfsimages/gfs.20091209/18/192/prectypeuktopo.png

Edited December 9, 2009 by THE EYE IN THE SKY

[weather eater]

Many saying they have never seen charts projected like this before so close ... I'm sure I have seen charts projected like this a few or more times over the years at similar timeframes - just that the promise has either gone pear-shaped or ended-up much less cold and snowy than progged, so worth bearing in mind.

However, haven't seen the models be this consistent over consecutive runs this far out with a blocked and cold pattern ahead with no real threat to break it ... so we could be on the verge of something special that we haven't experienced for a while - i.e. a protracted cold and potentially snowy spell.

I think your right to a degree nick, but not with this sort of consistency, right across the board. The crucial phase is over the next 4 or 5 days, the link up and formation of the GH. Who gets what snow and what day it arrives means nothing to me, I'll start thinking about that sometime late Saturday. You know what it’s like on here; as soon as the spell is locked in the agonising about the breakdown will start.

As much as I'm hoping for massive snowfall, I do worry for the more vulnerable, maybe it would be better if some stopped worrying about the whole thing falling apart and instead spared a thought for those who will struggle to cope if it does, one elderly client of mine is already feeling the cold and it’s been a balmy 11 or 12 degrees here today.

[kold weather]

OP, the only place that looks marginal on the 18z is EA by 180hrs which has the warm sector quite close by to it, but the NE would get hammered and IMO down to sea level as well given the nature of showers...of course modification of the flow will be an issue but thats still IMO cold enough for snow right down to SL.

[phil nw.]

Many saying they have never seen charts projected like this before so close ... I'm sure I have seen charts projected like this a few or more times over the years at similar timeframes - just that the promise has either gone pear-shaped or ended-up much less cold and snowy than progged, so worth bearing in mind.

However, haven't seen the models be this consistent over consecutive runs this far out with a blocked and cold pattern ahead with no real threat to break it ... so we could be on the verge of something special that we haven't experienced for a while - i.e. a protracted cold and potentially snowy spell.

Indeed Nick.I feel the letdowns in the past have probably come out of more marginal setups such as Scandi high`s under pressure from lower Arctic heights.

How often in recent years have we been excited to see a Greenland Block projected at this short range?

http://charts.netwea.../72/h500slp.png

The Steve Murr sausage of 552 up to Svalbard.

Edited December 9, 2009 by phil n.warks.

[Tom Montalbano]

A few grabs from the 18z Mean. Pretty stunning stuff.

http://91.121.94.83/modeles/gens/run/gens-21-1-144.png?18

http://91.121.94.83/modeles/gens/run/gens-21-1-180.png?18

http://91.121.94.83/modeles/gens/run/gens-21-1-240.png?18

Regards,

Tom.

[damianslaw]

Talking within the reliable timeframe first i.e. out to Monday it is now agreed that we will be under the influence of high pressure and fog and frost are going to become major players. Expecting some parts of central north england and southern england to see some stubborn fog this weekend supressing temperatures, however, the reliable timeframe is not yet showing the deep cold uppers that are being forecast for next week.

Must say though the teleconnections i.e.deep sustained negative AO and NAO suggest only one thing and that is for the high to retrogress to Greenland allowing the cold arctic air to steamroller in, it may be a stuttery start as we see the initial trigger in the form of low pressure tracking down the North Sea which intially may have a bit of mild air mixed in reducing chances of any precipitation being of snow at low levels especially near the east coast and more so in the SE, but the eventual outcome is looking increasingly like we will end up in the deep cold arctic uppers.

Too far out to call just how cold and snowy things will get, but the signals are increasing by the hour almost that a sustained cold and potentially snowy spell is on the cards.

On a personal note I love cold and love snow and my favourite synoptic would be what is being shown for later next week i.e. high pressure over Greenland and a lovely cold N/NE spell, won't get excited until it all comes into the reliable timeframe, but if it occurs as being shown - almost perfect synoptics for the run to christmas, it speaks sustained cold and alternating northerlies and easterlies, a synoptic we saw in classic winters of the past.

[LomondSnowstorm]

The snowfall in feb that im referring to didn't occur during the E,ly with those cold upper temps. The only snowfall that fell during that Sunday evening was the thames streamer that affected parts of london.

Here is the period im referring to and if you bothered to look at my sig you will note the 5th Feb!

http://www.wetterzen...00220090205.gif

Come on OP look at this objectively!

Edit I can't see mucn green on this chart.

http://charts.netwea...ctypeuktopo.png

Love the dark red diamond shape right over my house . Sorry to tempt fate or whatever but I'm beginning to feel like the cold snowy weather, at least for some parts, is going to occur, because I can't see any model support for any other conclusion! If the 00Zs keep the same pattern going, I feel that we can be fairly certain of at least some kind of snowy spell for much of the UK.

Enjoy the allnighter, for those who are brave enough, and I hope we aren't discussing the biggest downgrade in history tomorrow!

LS

[Nick F]

OP, the only place that looks marginal on the 18z is EA by 180hrs which has the warm sector quite close by to it, but the NE would get hammered and IMO down to sea level as well given the nature of showers...of course modification of the flow will be an issue but thats still IMO cold enough for snow right down to SL.

Some low H500-1000 thicknesses may help though ...

- t+180