Model Output Discussion - Tuesday 20:25 -->

[Optimus Prime]

Even in the reliable timeframe I could plausibly see snow flurries for the SE with -5 air flirting with the SE corner and an LP close by.

That's the 850 temperature which is 1500m above sea level, has nothing really to do with sea level temperature. Surface temperatures could be anything from -10c daytime max/min -27 (over snowcover and light winds) or +6c max/min 2c (over clear wet ground)

It's all pretty marginal at that stage.

[Thundery wintry showers]

Yes- I think with fronts moving south in a northerly flow and temperatures around freezing that would be the most widespread white Christmas since at least 1995 and probably since 1981.

The GFS and ECMWF are broadly agreed on a few days of dry, sunny and cold weather, followed by the arrival of a moderately cold ENE flow (from a continent that is only just starting to cool following a spell of westerlies). It would most likely start dry and cloudy, with a transition to sunshine and showers in eastern (especially south-eastern) areas as those -5C 850hPa areas spread into Britain. Showers would most likely fall as a wintry mix with accumulations restricted to high ground.

Then there is strong agreement that at T+168 a low moves south down the North Sea introducing progressively colder northerlies and, following behind, a very cold north-easterly, promising a mix of sunshine and snow showers, heavy and prolonged in eastern areas, and a widespread snow cover.

However we still need to have some caution here. The snowy outbreak is still 7 days away and the UKMO has thrown up a far more progressive solution with Atlantic systems powering in from the SW already by T+144 and the continental air not making it over. It looks a very unusual evolution for a situation which has an omega block just two days beforehand, but it shows how uncertain this thing still is.

[kold weather]

The models are starting to lose the balance thats been described IMO a little now, the UKMO is a great example of this and a fair few of the GFS ensembles overpower the high now as well, Scotland would be cold regardless but a fair few ensembles do lose the best of the cold.

Still if that was to occur odds would be high for a big snow event and with a southerly jet we could quite easily stay below average.

My fear is the UKMO however, I've seen that model be the cause of many a downgrade before when it jumps ship!

[Michael Fishermans Friend]

mmm not sure about the 06hrs GFS run, even when we get the 'link up' to HP to the NE as mentioned we have these short waves keeping the real cold from these shores for a further couple of days in a unreliable time frame. Overall the pattern still remains with HP to the North East/North but will we see real cold? I have to say the UKMO 0z looks completely different to the GFS/ECM.

[Guest North Sea Snow Convection]

Was that an intentional pun Tamara! The 850 -5 isotherm seemed to be held over Holland for what seemed like an eternity before it finally moved westward from the Dykes! The low actually takes about 2 days from the Norwgian coast to Belgium, probably under pressure from everybody shouting "Move South".

If that run verifies I would expect a rain to snow situation from the east.

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

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

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

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

We then get another low drop SW, with more widespread snow, which is then absorbed by the main low over the Bay of Biscay.

Then bitter easterly for the whole U.K and as the wind drops out some severe frosts would occur combined with snow cover. Hint of a re-load northerly towards Xmas day.

Stop! I'm getting way ahead of myself there but that has to be one of the best ever runs I've seen on the net.

No doubt its going to get colder and drier than it has been lately, no need to be specific about the fine detail, says he, having done just that!

A word of caution, its not in the bag yet, I will be more confident if these sort of runs are still occurring come Friday/Saturday. Its that t96 thing from past experience.

Regards,

Tom

Quite unintentional I'm afraid. Spelling usually never lets me down.

I think the 06z is playing on the possibilities of what part the north sea might play in terms of the boundary between the very cold arctic air to the north east and the relatively less cold air over the UK. However it is all conjecture and we will no doubt see all sorts of scenarios played out which subtly will make a great deal of difference in terms of temps, ppn etc to a small island like ours.

I agree about needing to wait another day or two till the variations on the the overall theme have settled. We still don't have total model agreement on the exact set-up - even though the -AO and northern blocking theme is a certainty now.

[NorthantsSnow]

That's the 850 temperature which is 1500m above sea level, has nothing really to do with sea level temperature. Surface temperatures could be anything from -10c daytime max/min -27 (over snowcover and light winds) or +6c max/min 2c (over clear wet ground)

It's all pretty marginal at that stage.

I know what the 850hpa temperature is, but thanks anyway. I agree, it would be marginal initially, that's why I said extreme SE could see snow flurries from that chart.

[Cecil Hogmanay Melchett]

The models are starting to lose the balance thats been described IMO a little now, the UKMO is a great example of this and a fair few of the GFS ensembles overpower the high now as well, Scotland would be cold regardless but a fair few ensembles do lose the best of the cold.

Still if that was to occur odds would be high for a big snow event and with a southerly jet we could quite easily stay below average.

My fear is the UKMO however, I've seen that model be the cause of many a downgrade before when it jumps ship!

I think i agree KW.Im starting to get the collywobbles here!

Whilst the op run was great a fair few ens now shunt the cold stuff east,as do the ecm ones to be honest.

The majority of runs bring cold but there is far to much of a split for my liking and add D Brett's comments

and a decidely dodgy ukmo run and i think there is enough to think,oh no,here we go again!!

Anxious times and im not sure if im looking forward to this evening.

[kold weather]

Also note the upper block transferring westwards, most of the time what you'll see is the block because west based, low pressure steadily mount an attack from the SW and unless you have a very southerly tracking jet indeed slowly you'll see a return to wet zonal conditions, of course not before you'd hopefully get a right whack from snowfall.

I think the odds are strong that the UKMO is too progressive, so we either have a short lived easterly, then a possible snow event as the lows move in, or we have a longer lasting block, and probably the same eventual outcome.

[NorthantsSnow]

mmm not sure about the 06hrs GFS run, even when we get the 'link up' to HP to the NE as mentioned we have these short waves keeping the real cold from these shores for a further couple of days in a unreliable time frame. Overall the pattern still remains with HP to the North East/North but will we see real cold? I have to say the UKMO 0z looks completely different to the GFS/ECM.

It is just one run though. I think it would be wise to see firstly what they have to say in their LRF this lunchtime (they might not necessarily go along with their own model) and then see what the 12z comes up with.

Basically, I wouldn't worry too much about the UKMO yet. 2/3 major models favouring something colder. If the UKMO persists with similar output then I would be concerned.

[Tom Montalbano]

Some grabs of the 06z mean at certain points.

http://91.121.94.83/modeles/gens/run/gens-21-1-114.png?6

http://91.121.94.83/modeles/gens/run/gens-21-1-144.png?6

http://91.121.94.83/modeles/gens/run/gens-21-1-168.png?6

And later in the run.

http://91.121.94.83/modeles/gens/run/gens-21-1-216.png?6

http://91.121.94.83/modeles/gens/run/gens-21-1-240.png?6

http://91.121.94.83/modeles/gens/run/gens-21-1-288.png?6

Pretty much keeping low pressure to our SW and the UK in a cold flow out into FI.

London 06z ensembles. Not at all bad!

Regards,

Tom.

Regards,

Tom.

[kold weather]

Yeah, the only worry is I've seen the UKMO clock new trends when the other have come onboard in similar evolutions and the UKMO has been the one to be correct and a few runs later the ECM/GFS clock on to it...UKMO certainly is the worst run bar none this morning.

The other thing that could happen is the shortwave develops to our east, then merges with the Atlantic low and we don't get the cold whilst the Atlantic low is swang round and towards the UK inducing SW airflow, a few of the ensembles show that problem and if the blocking does weaken quickly and withdraw to the west then thats a very real solution...of course the upside is if the high does stay locked in place then it would induce a VERY bitter ESE/E flow indeed.

[Guest North Sea Snow Convection]

The UKMO doesn't look convincing at the sudden leap and jump from t96 to t120 with the abrupt dearth of isobars over a large swathe of both UK and Europe. All the other models are consistent with keeping a solid high pressure wedge ridging strongly southwards with no retraction of the ridge right up to northern most latitudes like the UKMO.

Of course it can't be ignored, but it doesn't look plausible to me - far too fast surely.

[kold weather]

I'd have to agree Tamara in that respect, I think the UKMO is way too progressive with the set-up.

The models really are reflecting the phase 4 GWO though on thier output with low pressure powering up in the Atlantic on many runs, the ensembles are a synoptic mess past 168hrs, nearly every run has a different evolution with regards to the shortwave, some have us in a SW flow by 192hrs, some never get rid of the cold, some have a snowy breakdown, others you'll be lucky to get an hour of snow!

In truth, we are no closer to knowing what will happen and if anything things are even less sure then yesterday, though the odds of a snow event down the line are improving IMO if we can stay away from a UKMO solution.

[NorthantsSnow]

UKMO only goes out to T120?? Am i missing somthing here? Can some one post a chart of the ukmo with the worrying development on it as at the moment i have no idea what every1 is worried about?

The T144 chart is here:

http://www.wzkarten.de/pics/Rukm1441.gif

[Guest North Sea Snow Convection]

I'd have to agree Tamara in that respect, I think the UKMO is way too progressive with the set-up.

The models really are reflecting the phase 4 GWO though on thier output with low pressure powering up in the Atlantic on many runs, the ensembles are a synoptic mess past 168hrs, nearly every run has a different evolution with regards to the shortwave, some have us in a SW flow by 192hrs, some never get rid of the cold, some have a snowy breakdown, others you'll be lucky to get an hour of snow!

In truth, we are no closer to knowing what will happen and if anything things are even less sure then yesterday, though the odds of a snow event down the line are improving IMO if we can stay away from a UKMO solution.

Good summary there - and yes the GWO phase 4 orbit suggests an attempted return of the atlantic trough. Much as GP indicated as far back as a week or more ago, when anticiapting the vortex split etc and before the upcoming cold potential was even in the proper modelling and we were in the midst of dartboard lows.

The models will undoubtably over anticipate the next stage of the -AO block in respect of the returning atlantic trough and try to drive a wedge through it prematurely - imo. The UKMO is perhaps the first sign of this already happening.

Edit: the new METO update is very encouraging that their own model is indeed being too progressive.

Edited December 9, 2009 by North Sea Snow Convection

[Snowaddict]

I will agree that UKMO is a worry at T+144, but the Met Office seem to be rather confident & overall mean ensemble and deterministic guidance must be promising when you see a cold to very cold outlook with snow mentioned several times:

To me, they favour a blend of the ECMWF/GFS Operational solutions:

UK Outlook for Monday 14 Dec 2009 to Wednesday 23 Dec 2009:

On Monday, cold with slow-clearing mist or fog in the south and west although there is a risk of showers or outbreaks of rain, turning to snow over higher ground, in the north and east through the day. Remaining cold and mostly dry in many areas through the rest of the week although there is the potential for blustery wintry showers especially across northern and eastern parts. The nights will be frosty in many places with some persistent fog or freezing fog also forming. From Saturday and for the rest of the period it is likely to remain cold or even very cold and rather breezy at times. It could also turn more unsettled bringing a further risk of snow showers, especially to northern and eastern parts.

Updated: 1153 on Wed 9 Dec 2009

[kold weather]

Yeah though I'm a little surprised that its the UKMO of all models that brings in a progressive pattern, thats why I'm a little more worried then I'd be if it was the others as the UKMO tends to be very solid when it comes to that side of things.

Plenty of cold about on the models, then things look like becoming very messy and then it just comes down to luck as to whether the lows line up in a good way or bad way for the UK...

[Tom Montalbano]

Just read that Met Office update and has settled the nerves somewhat. Looks pretty good to me and we know from past experience that the METO dont throw the S word around lightly.

Courtesy of Reading, 3 of the last 4 GFS ensembles, dont have last nights 18z.

12z yday. http://meteocentre.com/ens/gfs_ens_rdg_t850_12.gif

00z. http://meteocentre.com/ens/gfs_ens_rdg_t850_00.gif

06z. http://meteocentre.com/ens/gfs_ens_rdg_t850_06.gif

Regards,

Tom.

[Methuselah]

Well, if the UKMO is really the WORST model we have on-offer today, I'd say that the near-future looks quite bright indeed. Shades, anyone?

[andy_leics22]

Interesting Ensembles. Quite a scatter but a lot going for below -5 on the Manchester one which is promising.

[stewfox]

Well, if the UKMO is really the WORST model we have on-offer today, I'd say that the near-future looks quite bright indeed. Shades, anyone?

Can anyone post again when the main models are due out

So those of us at work know when to 'pop in'

Edited December 9, 2009 by stewfox

[Snowyowl9]

All I can see today are huge upgrades a greenland high showing on every model that I`ve looked at.

Best GFS 0z run for years,ECM a great run.

The high goes further north friday/saturday.

http://91.121.93.17/pics/Rtavn1681.png

http://91.121.93.17/pics/Recm1441.gif

http://91.121.93.17/pics/Rgem2281.gif

Theres always one model that will dissapoint if you at too many,but this does look an odd chart.

http://91.121.93.17/pics/Rukm1201.gif

[Frosty.]

Well, if the UKMO is really the WORST model we have on-offer today, I'd say that the near-future looks quite bright indeed. Shades, anyone?

The only concern I have is that the real cold is being shunted further back by the latest models, as is the chance of snow, but there will be colder conditions setting in from friday with overnight frost and fog patches which will make temps struggle to rise much above 40f this weekend. Today is the last very mild day in the south, 13c in london, nearer 10c tomorrow then 7c by friday with downward trend continuing.

[Nick L]

Can anyone post again when the main models are due out

So those of us at work know when to 'pop in'

Add this to your favourites:

http://forum.netweather.tv/topic/25253-daily-chart-timetable/

[andy_leics22]

I don't buy the UKMO at all, I don't like the UKMO, GFS all the way for me

I'm not just saying that because it's showing better snow prospects than the UKMO, i've just never liked the UKMO. I remember when it predicted snow for large parts of the country before turning to turn overnight and the GFS said that it wouldn't even be snow when it started apart from high ground above 300m and the GFS turned out to be right and the BBC and Met-O had egg on their faces.