Model Output Discussion - 26Th Dec 21:25-->

[swfc]

Phew,was hopeing for a bit of an improvement even in the short term.????. Not to keen on the ukmo either.Blocking here there and everywhere.Jet going south and we still cant get that easterly flow across us.Good call by SM earlier regarding the shortwave,looks to be straw that breaks the camels back.Shame but there you go.Just to note the latest bbc graphics just showed the snow limit on wed up to north wales and across to the midlands.rain in the south.Slightly immaterial at this time scale but its not busy and im clutching at any straw.Sorry mods

Edited December 27, 2009 by swfc

[swfc]

Well well,ecm looks like its coming to the rescue,????.pesky shortwave moving away slightly at 120 hrs,the low is also further south. :rolleyes:Looks good mid term but loses its way towards the end.light eastily and could evolve with luck.

Edited December 27, 2009 by swfc

[cooling climate]

Major differences in the models from t168 the GFS 0z sends the block east over Scandinavia while

the ECM sends it west into Canada lol.

Plenty of disagreement still at close range as well.

Hopefully this afternoons runs will be more enlightening.

In fact massive differences in the post t168 range between the two models as the ECM throws up

a massive block into the Arctic above Alaska while there is no evidence of this at all from the GFS.

Edited December 27, 2009 by cooling climate

[leroys35]

like the ecm 216 and 240 lows heading in to france southern uk will get lots of snow from that path

[MR EXTREMES]

looking at the fax upto t120 it looks ok for midlands north perhapes just a little futher north.

but very very messy shortwaves near scandi looking like there going to ruin the party,

but this said the gh is very strong so maybe just maybe at little more time and we will see delayed but a true cold blast.

i think it will happen but not for awhile yet.

like the ecm 216 and 240 lows heading in to france southern uk will get lots of snow from that path

yes but confidence at that far out would be extremely low.

the only fear i have is that the cold is there but never makes it,

how many time we seen that happen over the last decade lol.

[KTtom]

As others have already mentioned some huge differences between the big 2 this morning. ECM tries its best to give us a blast from the east while the GFS looks odd to say the least, for some reason it has it in for the south west with a trough which seems determined to stay put and bury these areas under feet of snow!

All getting a little messey in the shorter term, the models are great for mid term pattern trending but for the immediate future I think i'll stick to the BBC, which this morning says 'turning much colder next week, as fronts try to move up from the south there could be some very heavy snow for parts of England and Wales'.

I think thats all the detail we will get today.

[Iceberg]

I think there is a little too much emphasis on the smaller scale meso happenings and perhaps we need to look at the bigger picture.

Here are the 3 N.Hemisphere models projections at the 144Z range and you can easily see how different they all are.

ECM has the PV lifting out of N.America over the arctic and into Scandy (There will be no real easterly with that happening). Due to the PV lifiting it then aggressively builds the High over N.America in it's place

GFS keeps and weakens the PV, splits it a bit but always leaves some of it in N.America, providing a completely different solution. This allows some pressure rises to our NE, But without the undercutting Jet to provide the easterly, it's essentially just a SE flow from an admittedly cold continent.

UKMET is something of the two, never really knowing what to do with the PV, so partially moves it out of n.america across the arctic to prevent a proper Easterly blast, but neither build the high over the N.America.

Even without the Ensembles we have very large disagreements about what's going to happen to our west (at the 120-144 range) and due to the fluidity of the N.Hemisphere at the moment this effects us very quickly within 2 days or so.

What does this tell us ? That anything beyond 144-168Z is highly uncertain and could vary widely, anybody that tells you that x or y is going to happen beyond that time is telling porky pies as they don't know.

What we do know is:

A southerly tracking jet.

High pressure to our north(either NE, N or NW).

So cold is at least a real possibility, which is an improvement on most years.

In the pre 144 range we also at least have a possible snow event for many people Thurs/Fri/Sat. (of the 3 ECM is the best IMO).

[carinthian]

No gloom from me this morning. All these models are producing great winter charts and we are less than 1/3 rd into the season. Look at the height rises over Greenland and to the Northeast. Great potential there. It does not matter about short waves in the vicinity of Scandinavia, they have always been there in this type of set up. The main thing is the cold air is become established with- in the British Isles ( look closer to home and note Scotland temps and cold block). Would not be surprised later today that the Altantic Lows are forecast to stay in Europe and fronts to not advancind beyond Southern Britain !!

C

[West is Best]

Remarkable short-range model variation. In general the GFS operational is somewhat out on a limb. Massive ensemble scatter and the operational on the mild fringe, with the ENS centring the low much further south:

Much of the GFS run looks synoptically bizarre to me, there's huge ensemble pressure variation, and I'm almost inclined to bin it. There are too many oddities to make it very plausible.

ECM is a fantastic run, with UKMO very acceptable. Absolute stand out is GEM again, which hasn't budged for days:

[Frosty.]

The GFS 00z is groan worthy and by T+180 hours there is mild air pushing into the southwest. Before then, it will be cold, especially in scotland and it would produce some snow in most areas but the long term pattern is towards less cold and then milder, we get one of those horrible SE'ly's which is neither cold enough for snow but feels roar and produces drizzle. The ecm 00z is a colder run with potential for reloads from either the north or east, the ukmo 00z looks cold out to T+144 but has a strange little ridge bulging north through england later. I really like the GEM 00z, a classic wintry run, especially for the north but not too shabby in the south either. With so many differences, we still don't have a clear enough trend beyond the next 72-96 hours.

[Weather-history]

Here's the UKMO 0z at 72hrs in more detail

Preciptation

Plenty of preciptation there

850hpa air

Chilly air North Wales, north Midlands northwards

Temperatures

With my amateur eye that looks like snow across at least northern parts.

Edited December 27, 2009 by Mr_Data

[TEITS]

Some very nice +120 charts on offer this morning.

http://www.wetterzentrale.de/pics/Rgem1201.gif

http://www.wetterzentrale.de/pics/Recm1201.gif

ECM upper temps.

Very little point going beyond that.

[keithlucky]

I see that the met office pressure charts show the front stalled over swales where does it show the front moving north? If this chart is correct sureley it shows northern blocking taking place.

[Grimsby Snow Lover]

I see that the met office pressure charts show the front stalled over swales where does it show the front moving north? If this chart is correct sureley it shows northern blocking taking place.

What I would also like to know is where the talk of snow is coming from for Tuesday. The 528 dam line is way to the north and the temps don't look that cold. Sorry if I have missed something here, but it has been something that was pointed out alot during the recent cold spell when talking about snow prospects.

[snowfish]

What I would also like to know is where the talk of snow is coming from for Tuesday. The 528 dam line is way to the north and the temps don't look that cold. Sorry if I have missed something here, but it has been something that was pointed out alot during the recent cold spell when talking about snow prospects.

Funny you should say that! I have been looking at the precipitation type charts for GFS and it looks like plain old rain (and cold rain at that) for most in the southern part of the country....

Grimsby Snow Lover is right in thinking that the 528 dam line is indicative of whether precip falls as either rain, sleet or snow?

Any thoughts anyone?

Edited December 27, 2009 by snowfish

[Grimsby Snow Lover]

Funny you should say that! I have been looking at the precipitation type charts for GFS and it looks like plain old rain (and cold rain at that) for most in the southern part of the country....

Grimsby Snow Lover is right in thinking that the 528 dam line is indicative of whether precip falls as either rain, sleet or snow?

Any thoughts anyone?

My take on the 528 dam is that when it is over the country the upper air temps are around -5 which support snow, when not they are nearer 0 which is much more marginal. This is why the posts on here are confussing me.

[MP-R]

Funny you should say that! I have been looking at the precipitation type charts for GFS and it looks like plain old rain (and cold rain at that) for most in the southern part of the country....

Grimsby Snow Lover is right in thinking that the 528 dam line is indicative of whether precip falls as either rain, sleet or snow?

Any thoughts anyone?

Well the 528 line doesn't seem to move properly south until Thursday-Friday. So it is almost undoubtedly going to be rain, some quite considerable rain too with temps of 2-4C in the south at first. Lovely.

[Duane S.]

Well if there is a 'missing data' issue then we should see that resolved today I suppose.

I have to say that some of the charts look quite simply like they got drunk/bored/tired as they went on. The GFS being the worst culprit.

The MJO and GWO have been freewheeling around from phase to phase over the past week so what the implication of this is for us exactly I'm not too sure? The MJO is heading towards phase 1, often not a good place to be but hopefully GP can put my mind at ease there.

The AO is currently tanked and looks set to remain so for a while yet and the NAO looks set to drop shortly as well. I'm not sure how well this is getting reflected on some of the chart showings though.

At the end of the day we still have all the energy going into the Southern arm of the Jet so the possibilities are there for us to tap into some real cold.

I have to say my confidence has taken a bit of a dent over the past 48 hours but that is as a result of spending far too long analysing every run! .If I'm honest I would say that today I think we will see the start of the upgrades. I just don't see how, with the synoptics and teleconenctions on offer, we do not see more classic runs appearing? I think that the block above us will start to ridge down more and that the cold air boundry line will cover the UK by next weekend courtesy of that LP tracking further south and clearing our shores quicker than is currently being progged. As for the SW off Norway I can understand SM's fears but these little shortwaves always pop up, even under strong Northerly blocking scenarios. With the right conditions (we are not there yet mind you) it shouldn't be more than a minor inconvenience. As opposed to a more knige-edge scenario whereby that SW really could mean make or break.

Of course I am fully aware though that cold synoptics and favourable teleconnections alone guarantee absolutely nothing. They merely increase your percentage of receiving cold weather here in the UK. With this sort of rare setup it's not so much that we need a sprinking of good luck (we shouldn't need that) we just don't want a great big dose of bad luck! Oh dear then.

Edited December 27, 2009 by s4lancia

[mcweather]

Before the 00z gfs run induces too much wrist slashing. Can I just remind everyone what the Met office who are always ultra cautious in there outlook are saying.

UK Outlook for Thursday 31 Dec 2009 to Saturday 9 Jan 2010:

On Thursday there is a risk of further sleet and snow in the south and east before it moves away southeastwards. This will allow a cold northeasterly flow to develop across the UK with wintry showers in northern and eastern areas. Some central and western areas enjoying drier, brighter spells. Staying frosty in many areas overnight. Friday and the weekend period look like being in a cold northerly flow with snow showers affecting many areas, especially northern and eastern areas. This will lead to a widespread and sharp frost. The following week looks cold especially in the north with wintry showers here, and possible rain, sleet or snow encroaching from the southwest at times. Overnight frosts are likely to continue.

Updated: 1204 on Sat 26 Dec 2009

Having lived through more winter spells than I care to remember. The one thing I have noticed is that the northerly extent of the encroaching fronts from the south are nearly always initially over egged and then corrected southwards as the degree of stalling is always difficult to forecast exactly. To my amatuer but nevertheless experienced eye. An extended cold spell is still very much on the cards.

[john mac]

well eyes down now for the next installment of fun and games. There shouldnt be any missing data issues with the models today.

Exciting times ahead with everything on a knife edge, i have a feeling that you mods are going to be very busy bees later today

fingers crossed everyone

[I remember Atlantic 252]

what times the next round of model output due out?

6Z trickling out now, www.meteociel.fr, or netweather data charts

[West is Best]

Sorry to sound stupid but howcum theres missing data around christmas then? do the models stop for a mince pie too ?

Lack of aircraft data I believe?

Re. the cold enough for snow debate, this is not just based on the 528 dam. Upper air temps, the stalling occluded front abutting the cold from the north and causing undercut are also major factors. If the front stalls then to the north of it will be snow. Had precisely this in Devon this February when it was, allegedly, going to be rain. All signs look fine to me. It will be marginal though: proper snowfall in southern Britain is ever thus.

Edited December 27, 2009 by West is Best

[TEITS]

ECM ensembles remain bitterly cold. Infact the mean is colder than yesterday.

http://www.knmi.nl/exp/pluim/vijftiendaagse/Data/15DAAGSE_06260_NWT.png

I will add that despite being unable to view the ECM +168 upper temps I reckon these would be between -10/-12C. The +168 might not look that cold but trust me it is!

[grab my graupel]

Models can be viewed here on Netweather

http://www.netweather.tv/index.cgi?action=nwdc;sess=

[Barb]

For my area, for snow it looks like this:

GFS op: Horrific

GFS ensembles: OK

ECM: Great

GEM: Great

UKMO: Poor

FAX: OKish

GME: Great

I sure don't know what'll happen.