Model Output Discussion

[MR EXTREMES]

http://www.wetterzen...00119630101.gif

Well I just took a random chart from January 1963 and the AO doesn't look positive to me with a strong PV to the north, however the Uk is still cold.

You shouldn't look at one teleconnection for the answer, they all need to be looked at and a forecast arrived. The AO is important in that it shows cold air spilling out of the Arctic however that is no guarantee it will knock on our doors, we need a -NAO to help deliver that as the above chart shows.

funny you say that because someone mention a neg nao earlier it may have been GP he also correctly predicted what the NOAA have said about the height movement and hes also outlined hes thoughts which to be honest very positive.

ive not seen the last charts im getting to this just got to read a few more pages but still looking good.

[Jan_Bromley]

We are kind of back to where we were earlier in the week when we we focussing on the cold spell starting after the weekend and the GFS and UKMO were pretty well agreed on snow potential from early in the week, but the ECM was much more cautious. The potential for that as we now know is much smaller and pretty low. However, here we are again looking ahead at 5/6 days again at what is a colder still scenario and thus far the GFS and now UKMO have given indications of a pretty wintry scenario for the post mid week period. Again 5/6 days. We wait for the ECM again to give its verdict.

The proper cold air relies on timing/phasing of the system to the north moving south quickly enough, and this will continue to play on the modelling through the weekend and start of next week before we can be much more certain what is going to happen. So assuming full agreement at 5/6 days away is achieved then this needs to hold through the weekend without any further glitches arising as the models play with this feature and what it is likely to do and how and where the cold advects to etc.

Getting past the 'jam tomorrow' situation remains the ever present hurdle atm - but the carrot is a huge reward for Thurs/Fri

Absolutely

[Edge of the moors]

How can it be nailed if it cant be nailed ??

With Araldite ?

[Alex95]

Looking at the models this evening, the 12z runs so far appear to be upgrading the snow potential for the NE quite considerably. I know it's a long way off, and you can't forecast snow accurately that far ahead, but it's hard not to get excited when the biggest snowfalls since 2001 (or even earlier) could be just round the corner.

Edited December 11, 2009 by alza

[John Snow]

If you think the synoptic setup is rife for snow, you might be disappointed.. the setup indicated will always bring drier air and lower dewpoints, of course if a precipitation event were to occur, then yet it would inevitably be as snow.

I'm not convinced hugely cold temperatures are going to occur from this though.

0 to -2C as night minimum is not conducive to an easterly of old.

So you don't think the GFS for Thu/Fri shows much if any snow for the areas that hit the shortwave (NE / Scotland) ?

[kold weather]

Interesting to see the models once again are starting to strengthening the shortwave, it has all but gone on yesterdays runs...

UKMO is a very good run, more progressive then the GFS but the cold looks solid, probably similar strength to the GFS, I'd imagine there'd be -10C in that easterly flow reaching the east by 144hrs...on a personal POV...I want the UKMO to be true as it reduces the time where the milder air is present by quite a lot.

Very good models, suggestive of decent snowfall in areas that normally gets them in easterlies.

My outside punt tonight...Boxing day 1962...as the northerly tries to come down the mild sector closes up as it hits the stubborn cold easterly air and the whole lot remains as snow, the 12z would show that if the front was stronger then it is on the 12z....

[TEITS]

If you think the synoptic setup is rife for snow, you might be disappointed.. the setup indicated will always bring drier air and lower dewpoints, of course if a precipitation event were to occur, then yet it would inevitably be as snow.

I'm not convinced hugely cold temperatures are going to occur from this though.

0 to -2C as night minimum is not conducive to an easterly of old.

Lets be honest though Stephen you wasn't convinced an E,ly would occur I seem to remember.

Anyway the min temps might not be especially low. Towards the end to the week a brisk E,ly wind spreading across a relatively warm N Sea will not result in low min temps because also there will be plenty of cloud cover with snow falling. However according to the 12Z upper temps do get as low as -13C in the SE!

[Duncan McAlister]

If you think the synoptic setup is rife for snow, you might be disappointed.. the setup indicated will always bring drier air and lower dewpoints, of course if a precipitation event were to occur, then yet it would inevitably be as snow.

I'm not convinced hugely cold temperatures are going to occur from this though.

0 to -2C as night minimum is not conducive to an easterly of old.

I would expect it to be colder than that under clear spells - when has the GFS 2m temps chart ever been accurate?

[kold weather]

If you think the synoptic setup is rife for snow, you might be disappointed.. the setup indicated will always bring drier air and lower dewpoints, of course if a precipitation event were to occur, then yet it would inevitably be as snow.

I'm not convinced hugely cold temperatures are going to occur from this though.

0 to -2C as night minimum is not conducive to an easterly of old.

Lower flows look like they are from the E/ENE so I'm not sure it'd be quite as dry as you think, and the GFS nearly always under-estimates the precip levels on an easterly, besides I'd have thought the lapse rates alone would probably be condusive along with some fairly low thicknesses.

I do agree with the cold issue though, I'm not sure it'll be the type of exceptional cold some people are thinking about, they usually come either with a mega cold blast (-15C and below at 850hpa) or when you've got a big snowpack on the ground already. Saying that some places will meet the second requirement and they probably will get some very bitter conditions, for most of the country I suspect though Friday's mins won't be far off thier maxes either...

[Snowaddict]

Eastern Ireland could do VERY well from both of the setups modelled by GFS & UKMO @ T+120 & T+144...

GFS 12Z is all round a fantastic run.

However, we've been here before & anything past T+96 should be taken lightly at the moment..

Right now I would say that both of the above 12Z's have come somewhat into line with the overnight ECMWF evolution.

IF & it's a big IF - it plays out as shown on the latest guidance then snow will be on the way, for many.

Either way it's starting to and will get rather cold to perhaps very cold as we continue forward.

There is also a growing consensus for a third cold incursion from due north as we head towards Day 8 - Day 10...

[Geordiesnow]

We are kind of back to where we were earlier in the week when we we focussing on the cold spell starting after the weekend and the GFS and UKMO were pretty well agreed on snow potential from early in the week, but the ECM was much more cautious. The potential for that as we now know is much smaller and pretty low. However, here we are again looking ahead at 5/6 days again at what is a colder still scenario and thus far the GFS and now UKMO have given indications of a pretty wintry scenario for the post mid week period. Again 5/6 days. We wait for the ECM again to give its verdict.

The proper cold air relies on timing/phasing of the system to the north moving south quickly enough, and this will continue to play on the modelling through the weekend and start of next week before we can be much more certain what is going to happen. So assuming full agreement at 5/6 days away is achieved then this needs to hold through the weekend without any further glitches arising as the models play with this feature and what it is likely to do and how and where the cold advects to etc.

Getting past the 'jam tomorrow' situation remains the ever present hurdle atm - but the carrot is a huge reward for Thurs/Fri

Regarding the end of the weekend easterly, this was only really predicted by the GFS, whilst the UKMO/ECM never trended towards the GFS. Actually if the GFS kept to what it was showing before it started showing those easterly charts, then this model would of been accurate.

As we all know though, more runs are probably needed as we have not got that much room for error, if those lower heights to the North prove to be stronger than first predicted, it would sink the easterly quite quickly. Conversely, if the lower heights to the South remain firm and the lower heights to the North don't make an impact to much, then we might get a longer easterly and a stronger one.

[Snow Queen one]

Well it was to be expected i said the other day i thought these charts for the SE were too good to be true and it has proved to be the case especially for Monday. I hope the cold does indeed arrive by the end of the week but as so many have said it is outside the reliable time frame and can easily get downgraded plenty of time to go yet.

The Precip charts on the NWExtra do look good though for Friday but should be taken with a pinch of salt i thinks. lol

[mcboz]

The CFS monthly 2m temp chart has changed it's tune in the last few days (most areas had 0.5 - 1.0 above average a few days ago, now most of Europe is blue!). Amazing really, show's how everything can change so quickly. Hopefully it doesn't change back!

http://www.cpc.noaa.gov/products/analysis_monitoring/lanina/images/euT2mMon.gif

[phil nw.]

We are kind of back to where we were earlier in the week when we we focussing on the cold spell starting after the weekend and the GFS and UKMO were pretty well agreed on snow potential from early in the week, but the ECM was much more cautious. The potential for that as we now know is much smaller and pretty low. However, here we are again looking ahead at 5/6 days again at what is a colder still scenario and thus far the GFS and now UKMO have given indications of a pretty wintry scenario for the post mid week period. Again 5/6 days. We wait for the ECM again to give its verdict.

The proper cold air relies on timing/phasing of the system to the north moving south quickly enough, and this will continue to play on the modelling through the weekend and start of next week before we can be much more certain what is going to happen. So assuming full agreement at 5/6 days away is achieved then this needs to hold through the weekend without any further glitches arising as the models play with this feature and what it is likely to do and how and where the cold advects to etc.

Getting past the 'jam tomorrow' situation remains the ever present hurdle atm - but the carrot is a huge reward for Thurs/Fri

Hi Tamara,

Yes well said.I am sure many of us are excited by the current outlook but it`s easy to get ahead of the game when detailed sypnotics cannot be pinned down yet.

Looking closely at the 06Z and 12Z GFS small but important differences appear as early as T72hrs.

Note the modelling of the s/w coming from Scandi and the way the High over the UK starts to ease away,altering the orientation of the Easterly flow.

Go forward to T144hrs.and we can is why Thurs/Fri`s weather has upgraded for want of a better phrase.

http://charts.netweather.tv/gfsimages/gfs.20091211/12/144/h850t850eu.png

http://charts.netweather.tv/gfsimages/gfs.20091211/06/150/h850t850eu.png

The moral being beyond T60-72hrs. range tiny changes in the surface flow will change run to run in this situation so let`s keep those sledges in storage for now and look again Mon/Tues.ie closer to the expected event.

Having said all that,(i am off my soapbox now)the overall set up going forward for next week is very good for colder weather to stay around for some time.In this pattern it`s only a matter of time before many see lying snow.

[snowmadchrisuk]

Overall very good this evening , I would just like to say I can still see Snow showers in the midlands on Sunday , I can't see why nobody else is picking up on it , -5 850 , 528 dam and precipitation over the Midlands all night into Monday according to the latest UKMO charts. Does anybody else see this or is it just me ?

Chris

[Barometer Obama]

The rollercoaster continues.

It looks to me like any precipitation on wednesday would be rain/sleet but then snow more likely thursday onwards.

I think patience is going to be the key, the Greenland high is virtually a dead cert and this should deliver.

[Yeti]

Overall very good this evening , I would just like to say I can still see Snow showers in the midlands on Sunday , I can't see why nobody else is picking up on it , -5 850 , 528 dam and precipitation over the Midlands all night into Monday according to the latest UKMO charts. Does anybody else see this or is it just me ?

Chris

I think it's just you - looks far too mild to me:

http://www.wetterzentrale.de/pics/Rtavn4817.png

We'll have to wait till next week with the colder uppers and lower heights (hopefully) until any real snow potential begins. Wednesday/Thursday looking the best so far for the UK but remember the position of the shortwave is changing quite a lot so the whole setup could end up a few hundred miles further S still (like the 6z).

Edited December 11, 2009 by Yeti

[snowmadchrisuk]

I think it's just you - looks far too mild to me:

http://www.wetterzentrale.de/pics/Rtavn4817.png

We'll have to wait till next week with the colder uppers and lower heights (hopefully) until any real snow potential begins. Wednesday/Thursday looking the best so far for the UK but remember the position of the shortwave is changing quite a lot so the whole setup could end up a few hundred miles further S still (like the 6z).

There max temps though , I would not at all be shocked if some flakes were reported somewhere in the Midlands or the SE on Sunday/Monday.

Edited December 11, 2009 by snowmadchrisuk

[kold weather]

Yep Phil, and really small changes will make a big difference to the flow down the line, esp for the SE, a small difference means a warm sector followed by a ESE wind and thus snow at all, whilst another change only gives a small warm sector and 48hrs of nonstop easterlies which is obviously a snow set-up...

Equally watch the Atlantic low with which its going to merge with, that will be just as important for the eventual attempted easterly...but it would be very hard to avoid an easterly I have to say.

BTW, for a stunning run, look at P7 of the GFS ensembles, very cold high pressure cell, then it lifts northwards and brings in an easterly, that is what we saw occur with the severe wnters of the past.

[Matty M]

Synoptics looks good, however i am quite concerned at poor depth of cold that does arrive, 850hpa temps of -6 to -8c dont necessarily = snow.

[Guest North Sea Snow Convection]

Hi Tamara,

Yes well said.I am sure many of us are excited by the current outlook but it`s easy to get ahead of the game when detailed sypnotics cannot be pinned down yet.

Looking closely at the 06Z and 12Z GFS small but important differences appear as early as T72hrs.

Note the modelling of the s/w coming from Scandi and the way the High over the UK starts to ease away,altering the orientation of the Easterly flow.

Go forward to T144hrs.and we can is why Thurs/Fri`s weather has upgraded for want of a better phrase.

http://charts.netwea.../h850t850eu.png

http://charts.netwea.../h850t850eu.png

The moral being beyond T60-72hrs. range tiny changes in the surface flow will change run to run in this situation so let`s keep those sledges in storage for now and look again Mon/Tues.ie closer to the expected event.

Having said all that,(i am off my soapbox now)the overall set up going forward for next week is very good for colder weather to stay around for some time.In this pattern it`s only a matter of time before many see lying snow.

Evening Phil.

Yes, that is a good post and documents nicely the subtle changes in modelling that we must all expect to see a lot more of in the coming few days ahead. I think if folk keep that in mind then it might be easier for some folk to avoid nick sussex classic car crash of emotions that he sometimes refers to

But if we can finally land the prize then as you say it does look a formidable pattern that is not going to give up the ghost easily at all. On that basis prospects for xmas itself are also getting more and more interesting. So perhaps a slight delay and further patience will be totally repaid!

Edited December 11, 2009 by North Sea Snow Convection

[cyclonic happiness]

There max temps though , I would not at all be shocked if some flakes were reported somewhere in the Midlands or the SE on Sunday/Monday.

Even 3 days away, precipitation predictions can change drastically and the temps are maxes, there could be evaporative cooling if it comes in as rain then turns to snow as it drags the cold air uppers down.

This has happened loads here in the midlands, last year we had the same thing and that all turned to snow even though the uppers weren't as good and everyone said it would be sleet at most.

[kold weather]

I doubt any showers will be strong for that to occur CH, pressure is fairly high and the lapse rates are probably not going to creare too beefy showers, though there wil lbe some about I suspect they wil lbe mainly sleety in nature...not something I'd pin any hopes on put it that way!

Anyway ensembles really are trying thier hardest to get rid of this pattern by the 20th by lowering heights over Greenland then not getting the upper low over Scandinavia far enough south as to couteract the LP in the Atlantic, and that becomes the dominant factor again as per phase 4 of the GWO. However as Tamara has just said, the set-up will be stubborn and I have strong doubts as to whether the set-up wil lbreak down as quickly as the ensembles are trying...I strongly suspect the old GFS habit of being too progressive is coming into play but wil lbe interesting to see if the 12z ECM does the same or not.

[snowmadchrisuk]

Even 3 days away, precipitation predictions can change drastically and the temps are maxes, there could be evaporative cooling if it comes in as rain then turns to snow as it drags the cold air uppers down.

This has happened loads here in the midlands, last year we had the same thing and that all turned to snow even though the uppers weren't as good and everyone said it would be sleet at most.

I remember , i'm not that far away from you . I'm just pointing out it might be one of them situations that catch some weather men/woman out.

[timistry]

Synoptics looks good, however i am quite concerned at poor depth of cold that does arrive, 850hpa temps of -6 to -8c dont necessarily = snow.

So am I. Precip will never make it to the west either i reckon. Any chance of anything from the atlantic i wonder?