Model Output Discussion

[weather eater]

Interestingly enough the 06z resembles some of the recent parallel runs, however the 06z parallel has dropped that idea and keeps the bitter cold going right to the end, the low approaching from the south west stalls and sinks and after a return to an easterly regime, it sinks an LP that has looped over Greenland right down across the UK, fantastic stuff.

[TEITS]

I love the evolution on this run - really like the way the north-east attack comes back in, and then further attacks from the south-west. That's precisely what we need. I don't want an arid boring easterly. For big snow events we need a really cold but unstable picture. That's why 1978/9 is so much more interesting than 1985/6. So bring this run on - it's excellent.

You will love the Parallel run as this keeps the cold spell locked in for the entire run. I will also repeat what I said a week ago.

Many assume the SW England escapes much of the cold, snow which is true to a certain extent. However given the right synoptics the SW can experience some of the most severe blizzards as were seen in the famous winters. This is why your right in what you say this is precisely what we need.

[Thundery wintry showers]

Looking through the models, once again the ECMWF has gone for a somewhat watered-down solution- the high stays close to Britain and most places would stay cold and dry on the basis of that run, with a few sleet/snow flurries for the SE early in the run, and the NE late in the run.

The GFS run brings the easterly air in sooner but the coldest air struggles to reach us- the cold air we pick up from the east is mostly relatively moderate stuff that is currently forming over the continent due to lack of Atlantic influence- and then the shortwave heading S down the North Sea is delayed and struggles to bring the coldest air in. Still, I would expect widespread falls and accumulations of snow away from the east coast from early next week onwards (probably a haily, sleety mix by the coast itself) from that setup.

UKMO looks similar to yesterday's runs with a relatively half-hearted ENE'ly to begin with (a wintry mix of showers towards the SE) and then a shortwave moving south bringing in the very cold north-easterlies.

It is notable that all three models keep cold, and potentially snowy, synoptics going right until the end of the run. The ECMWF shows that a cold but mainly dry outlook is still possible, and so while my estimation of the chances of a snowy spell has inched up to 60%, I am still feeling quite wary of that possibility.

[cooling climate]

The operational and parallel runs of the 06z GFS offer rock solid support for each

other out to t168+(FI).

As others have said excellent,excellent runs.

Daytime temps of around freezing fresh to strong east/southeasterly wind,windchill

down to about -8c perhaps lower and snow.

Later in the run a real threat of disruptive snowfall but thats to far out to worry

about for now.

Because of their strong support for each other I would expect the Euro's to follow

suit tonight.

[Iceberg]

The GFS alternative has snow almost everyday from the 14th to the 25th(and then that's just because the run stops ! ).

Monday isn't far away now and thats when the fun starts.

[smich]

I'm tempted to say "nailed on' but I won't just yet. However what we are seeing currently at say T84 has been showing run after run after run for at least two days, maybe three. And that's every model - excellent agreement now.

Could ALL the models backtrack now, within 48 hours of it all kicking off? Unlikely.

Hats off to the GFS especially. These charts were appearing in FI two weeks ago and have appeared ever since.

-NAO and an absolutey tanked -AO (off the chart) = Holy Grail.

smich

[Thundery wintry showers]

You will love the Parallel run as this keeps the cold spell locked in for the entire run. I will also repeat what I said a week ago.

Many assume the SW England escapes much of the cold, snow which is true to a certain extent. However given the right synoptics the SW can experience some of the most severe blizzards as were seen in the famous winters. This is why your right in what you say this is precisely what we need.

...as was well demonstrated last winter (Okehampton had 55cm, and even Exeter had two notable snow events). Sounds like February 1978 was especially impressive in the SW- if we can get a very cold easterly flow established over Britain (note the "if", as per caveats in my above post) then a repeat of February 1978's kind of setup would not be implausible.

[Iceberg]

I think limited snow and cold is nailed as this is progged for Monday from both the shorter term models.

There is still uncertainty about any major snow events (which does seem likely).

And prolonged cold (which seems less likely, but still possible).

The GFS ENS will be important again as always for the 06Z.

[kold weather]

I agree with you TWS, odds of cold seem just about nailed on at least till 180hrs (though I am wary about the 06z GFS set-up trending northwards, which would be the utter worst case!) however the synoptics are still not being really agreed upon.

What is noticeable however is the fact that the models are keeping the upper high over Greenland now and not rapidly transferring westwards, this opens up the door for an even more sustained cold shot.

In the end the shortwave will either make or break this set-up it seems, very uncertain IMO and could easily trend the wrong way as well as the right.

[phil nw.]

Looking at the wider picture for a minute.

The ECMF/GFS 8-10 mean Ht.comparisons.

http://www.meteo.psu...0z/hgtcomp.html

It can be seen that the GFS the block is further West and with more undercutting.

It does invite battleground scenarios from the South West later at the risk of milder air moving in from that direction at some point.

This i guess is where any breakdown would start from.

We would get some snow events from this pattern but as Kold has said it`s a higher risk stragedy.

The ECM if it were correct would be a potentialy longer lasting cold spell with the block nearby and keeping the lows well South.

It would still get v.cold but less snowy but with clearer skies some hard frosts.

Ideally we would want a middle way for cold to last.Cyclonic approaches from the South that stall but also the flow brisk enough to bring in the snow showers at times too.

This is what happened in the Classic Winters of 47/63.

Interesting times ahead.

Edited December 10, 2009 by phil n.warks.

[Thundery wintry showers]

My biggest concern for snow prospects would be the ECMWF as per my above post and I'm surprised so few people have picked up on it. It is quite similar to yesterday's 00Z run in many respects, and certainly a downgrade on yesterday's 12Z (though an upgrade on yesterday's 00Z). I am not too concerned about the GFS trending the setup north- true, it might lead to downgrading of longer-term prospects but it also increases the potency of an easterly outbreak early next week.

I certainly advise caution to those saying a snow event is nailed on. The ECMWF output would not produce widespread snowfalls.

[Shiny_Bottom_1]

Would agree with Ian on this one, re: snowfall.

GEFS ensembles for PPN (taking Deryshire, E. Sussex and Kent) are all very low. One or two members going for 'something' but overall, looking quite dry (btw, op run is, whilst not what I would call an outlier, in general, is rather optimisitc in terms of rainfall).

[kold weather]

Taking a leaf out of GP's book again I'd sugges the ECM is onto the wrong idea and is not showing nearly enough of an attack from the SW, the GWO phase 4 as GP has argued before strongly favours an Atlantic trough and yet the ECM once again tries to raise heights just to our west by 216hrs..I'm willing to bet that will not come off and the GFS will be closer to the mark, though it may also be overdoing it a little.

[Cecil Hogmanay Melchett]

This is fascinating.KW picked up on something yesterday and that is the low dropping through scandy merging with

a system developing to the SW,thats FI so most certainly subject to changes but one to watch for sure.

06z is fantastic for nothern Britain,but the brutal truth is its getting into twitchy bum territory for those

in the south.

Its going to get cold,i think thats a given,just how cold and for how long is very much undertain.

[weather eater]

You do have to suspect the ECM; if it picked a trend and stuck with it then it would have to be taken seriously, however at the moment it’s teetering between support for the GFS and rather random stabs at an alternative evolution. While it would be unwise to dismiss it completely it does not inspire confidence. As for the ideal evolution then the parallel has it, classic approaches from the SW rebuffed by the strength of the high.

[rowieboyz]

...as was well demonstrated last winter (Okehampton had 55cm, and even Exeter had two notable snow events). Sounds like February 1978 was especially impressive in the SW- if we can get a very cold easterly flow established over Britain (note the "if", as per caveats in my above post) then a repeat of February 1978's kind of setup would not be implausible.

We certainly can get hammered in that sort of set up! Models still look good this morning but I have seen it all go breast up very quickly before. I am just looking forward to a more seasonal feel to the weather, if we get any of the white stuff then that is a bonus.

Jase

[Pennine Ten Foot Drifts]

Honestly, how can anyone even dare to complain about a run which has this at T114:

followed by this at T138:

I think people forget how this compares to what we're usually served up. For example, this period last year:

I for one think any griping about current output is churlish at best !!!

[kold weather]

The best thing for the south would be for the shortwave to actually longer HD, then when it does possibly merge with the Atlantic low it;d already be on the west side of the low and that would mean the cold air would tuck in right behind the shortwave...instead if it happens too soon then milder air will surge up from France and then it becomes a matter of whether the cold air underneath it is strong enough...

Some of the ensembles look like they'd give a freezing rain/ice event to the south whilst snow further north...others keep the low further south and we keep a snowy easterly, and a couple look like total synoptic outliers past 240hrs.

ps, remember it can snow pretty much upto 0C at 850hpa in a cold continental flow and thats what we'd have on the 06z and a fair few of its ensemble members.

Edited December 10, 2009 by kold weather

[Thundery wintry showers]

Actually I agree with the above two posts. The ECMWF's handling of the shortwave in particular looks somewhat suspect to me, and it is certainly being a lot less consistent than either GFS or UKMO (the UKMO's 00Z yesterday appears to have been a one-off, apart from that it's probably been the most consistent of all).

I must admit that my references to the ECM are partly in order to keep my own "rampometer" at ground level because, as far as both Norwich and Cleadon go, an east-north-east flow from a cold continent is as good a "thundery wintry showers" (lol!) setup as it gets. Even if there isn't a major snow cover from it, the convection if any of these runs came off would most likely be very impressive near the east coast.

I have to agree that precipitation totals for central and western areas are uncertain even if we do get a pronounced easterly but that is normally the case. Troughs and/or very pronounced shower activity are usually needed to get many of those showers across to western areas- I believe they managed it on the 2nd February 2009 which had a remarkably showery easterly outbreak.

Edit: All this discussion about detail post T+192 isn't really worth it at this stage because there is so much uncertainty past T+96, well before we even get there. I'm not sure that the delaying of the shortwave is a good thing for cold/snow lovers though, as it could end up being delayed for too long before the lows start coming in from the SW- in contrast if it has already unleashed a very cold north-easterly by then (as per yesterday's 12Z runs) we will already have very cold air for the Atlantic to do battle with.

Edited December 10, 2009 by Thundery wintry showers

[Optimus Prime]

A poor performance indeed from the ECM...it really can't get to grips with this at all can it?

The easterly shown by the GFS is better then on previous runs and colder as well. The NE'rly is still very much a marginal situation.

GFS got it right IMO.

[Methuselah]

That southward-sinking 'warmer' sector forecast for midweekish next week is interesting. With all that residual dry cold air languishing over England ahead of it, I'd expect/hope to see some quite widespread (though probably not heavy) snowfalls as a result...Wasn't the snowfall of Boxing Day 1962 the result of something similar?? Indeed, would the 'warm' sector be long-lasting enough to cause much of a thaw??

All very interesting...The devil is in the detail!

[weather eater]

Actually I agree with the above two posts. The ECMWF's handling of the shortwave in particular looks somewhat suspect to me, and it is certainly being a lot less consistent than either GFS or UKMO (the UKMO's 00Z yesterday appears to have been a one-off, apart from that it's probably been the most consistent of all).

I must admit that my references to the ECM are partly in order to keep my own "rampometer" at ground level because, as far as both Norwich and Cleadon go, an east-north-east flow from a cold continent is as good a "thundery wintry showers" (lol!) setup as it gets. Even if there isn't a major snow cover from it, the convection if any of these runs came off would most likely be very impressive near the east coast.

I have to agree that precipitation totals for central and western areas are uncertain even if we do get a pronounced easterly but that is normally the case. Troughs and/or very pronounced shower activity are usually needed to get many of those showers across to western areas- I believe they managed it on the 2nd February 2009 which had a remarkably showery easterly outbreak.

It's certainly one of those times when I wished I was back living in my native Norwich, described to me by one Yorkshireman during a bitter easterly spell, as the coldest place he'd ever been. I'm really hoping the parallel comes off, just because for me it has been the most consistent operational it's not blinked once.

Edited December 10, 2009 by weather eater

[kold weather]

Edit: All this discussion about detail post T+192 isn't really worth it at this stage because there is so much uncertainty past T+96, well before we even get there. I'm not sure that the delaying of the shortwave is a good thing for cold/snow lovers though, as it could end up being delayed for too long before the lows start coming in from the SW- in contrast if it has already unleashed a very cold north-easterly by then (as per yesterday's 12Z runs) we will already have very cold air for the Atlantic to do battle with.

Whilst I do agree that faster would be better overall we could get caught with the shortwave opening up whilst over northewrn parts of the UK and the low just in the wrong position to our SW and all the shortwave would do is to help drag the other low too far north and dragging the milder air up with it, there are a couple of ensemble members that do that and look terrible for the south, the north would probably be pretty fail safe in this set-up IMO if that came off...however your right its still a long way off.

[Optimus Prime]

Lol Pete, we should really add a 1c-2c maybe 3c discrepency on 1962. The climate is warmer- right?

[Iceberg]

The 06Z Ensembles are out and keep the mean 850's below -5 for the entire run from next week onwards(for Wiltshire in central southern England), however there is more uncertainty about what exactly will happen.

More agreement would be nice.