General Model Output Discussion

[Guest North Sea Snow Convection]

As far as I can see the programme up to the weekend is the same and after this trough clears there is a good chance of snow showers for many in eastern and south eastern parts. What is disappointing is that the easterly does not evolve beyond Friday as has been suggested in recent modelling and the coldest air is yet again held back to the east. It does look like a bit of a repeat of the last cold spell in quite a few respects However, this is till some disagreement about the pattern from the weekend onwards and certainly regarding any breakdown, this is such a long way off and indeterminate, it is not worth discussing atm

[kold weather]

The 06z once again brings the high more to the SE which then builds back over the UK, thats what we really want to see and its a trend I think will continue once the PV over Scandinavia reduces and the bigger PV lobe starts to strengthen once more.

The models certainly are suggesting the PV powering up over the pole but we shall see what the end result will be, thats some way away just yet.

[azores92]

850mb temperatures of -8 to -11 across the UK & Ireland, several chances for snow showers beforehand into both Eastern Ireland, Eastern UK & Scotland. In addition, a feature to be watched towards T+120/T+132 that could potentially bring snowfall to southwestern parts.

sorry, but i just cant see much snow potential for eastern parts of ireland, away from exposed coasts, and exposed hills. snow from an easterly is always going to be tricky, as the colder air has a longer fetch from the continent to get there, and most showers die out by the time they reach wales. from a northerly, and the derry, donegal and antrim coasts will pick up snow showers, but not much further than that.

[beng]

As far as I can see the programme up to the weekend is the same and after this trough clears there is a good chance of snow showers for many in eastern and south eastern parts. What is disappointing is that the easterly does not evolve beyond Friday as has been suggested in recent modelling and the coldest air is yet again held back to the east. It does look like a bit of a repeat of the last cold spell in quite a few respects However, this is till some disagreement about the pattern from the weekend onwards and certainly regarding any breakdown, this is such a long way off and indeterminate, it is not worth discussing atm

The shortwave to the North on Saturday kills the easterly flow meaning the window for snowfall here is very short indeed. Without a pressure rise over Scandinavia to push the cold air to our East our way, then it's unlikely to be in a hurry to reach us - but even so it's going to be quite a cold snap - and always the prospect of a bit of snow here - but we'll need some luck IMO given the current model output and the tendency of the NAO pattern to be just slightly too far West for us at the moment.

[Paul]

(Another) reminder - this thread is for more detailed model discussion, more light hearted model chat (with things such as "this run is an upgrade", "this run is amazing, it's going to snow" etc) can be found here:

[Snowaddict]

sorry, but i just cant see much snow potential for eastern parts of ireland, away from exposed coasts, and exposed hills. snow from an easterly is always going to be tricky, as the colder air has a longer fetch from the continent to get there, and most showers die out by the time they reach wales. from a northerly, and the derry, donegal and antrim coasts will pick up snow showers, but not much further than that.

Hi Azores92

Plenty of snowfall potential for eastern Ireland from this Thursday through to Friday.

The overnight ECMWF run clearly models this from Thursday into Friday, with more organised snow at times. A strong easterly/northeasterly always delivers for Eastern Ireland.

Take February for example - copious snow showers off the Irish sea. With cold to very cold 850mb temperatures, instability and strong northeasterly winds, these snow showers will affect many parts of the east and southeast in Ireland. The other difference is that this is a Northeasterly and in essence the fetch is not so long.

If it was a due easterly then yes it would be much more difficult, but still the Irish Sea is a great generator for snow showers for Ireland - in fact it is one of the only ways in which eastern Ireland can get meaningful snowfall.

This is also modelled quite well on the 06Z GFS Operational run.

SA

[Lewis]

Fantastic 06z, with the cold pool establishing it's self, they would be some record breaking temps if that came off, for many eastern and N areas.

I would not call it a dry run, as the North Sea at the moment is a shower machine with warmer SST'S.

They could also be an event 3/4 way through the run where a band of heavy snow pushes from the WSW a little like the December 2005 event, but it quickly shows the cold air pushing back West, with the Atlantic loosing out.

Fantastic models,

Models at there best!!

Lewis

[Snowly does it]

06z one of those rather memorable runs with 384 hours of bitter cold ending with what would probably be the blizzard of the century and setting up perhaps a notably cold 2 weeks of January.

NErly switches to Greenland block and Arctic northerly which slips down over the UK with some still and bitterly cold weather and builds back into Scandi which gives a week of classic battleground mild versus cold with a deep LP system bringing snowmageddon as it crashes into frigid air.

Deal or no deal?

[nick sussex]

The 06z once again brings the high more to the SE which then builds back over the UK, thats what we really want to see and its a trend I think will continue once the PV over Scandinavia reduces and the bigger PV lobe starts to strengthen once more.

The models certainly are suggesting the PV powering up over the pole but we shall see what the end result will be, thats some way away just yet.

Yes i think this maybe due to the eastern USA trough edging ne which is expected to happen later in the outlook, this should have the effect of edging the block a little further east.

[Guest North Sea Snow Convection]

The shortwave to the North on Saturday kills the easterly flow meaning the window for snowfall here is very short indeed. Without a pressure rise over Scandinavia to push the cold air to our East our way, then it's unlikely to be in a hurry to reach us - but even so it's going to be quite a cold snap - and always the prospect of a bit of snow here - but we'll need some luck IMO given the current model output and the tendency of the NAO pattern to be just slightly too far West for us at the moment.

Yes that is a correct analysis, it did look like the Greenland High would extend far enough east towards Iceland, as well as linking up with heights towards the Siberian arctic in terms of sustaining an easterly or north easterly airstream for longer. Indeed there were promising signals on some of the modelling up to last night that this would happen. These spoiling shortwaves that keep tracking down from the north were a feature of the last cold spell and scuppered longer term snow potential for this part of the UK. As you say, the whole pattern is too west based in that respect and will keep favouring north western parts of the UK rather than southern eastern areas - with a tendency for troughs to pull the winds round to the north west or even west on the southern flank of the low pressure.

However, the overall picture certainly remains a cold dominated one - and no real signal that this is going to change - irrespective of the fact no doubt that the models will try and prematurely break it down

Edited December 29, 2009 by North Sea Snow Convection

[Snowaddict]

GFS Control @ T+126 also shows that feature approaching from the southwest, running into very, very cold air..

Something to be definitely watched as we go ahead nearer to the timeframe:

http://www.meteociel...ode=0&runpara=0

EDIT: Out to T+144 & it has outbreaks of snow quite widely across the UK in a strengthening easterly wind!

SA

Edited December 29, 2009 by Snowaddict

[dallas]

Surely the main thing is to get this cold to v.cold air really entrenched, then any bouts of PPN should make things interesting

[beng]

Yes that is a correct analysis, it did look like the Greenland High would extend far enough east towards Iceland, as well as linking up with heights towards the Siberian arctic in terms of sustaining an easterly or north easterly airstream for longer. Indeed there were promising signals on some of the modelling up to last night that this would happen. These spoiling shortwaves that keep tracking down from the north were a feature of the last cold spell and scuppered longer term snow potential for this part of the UK. As you say, the whole pattern is too west based in that respect and will keep favouring north western parts of the UK rather than southern eastern areas - with a tendency for troughs to pull the winds round to the north west or even west on the southern flank of the low pressure.

However, the overall picture certainly remains a cold dominated one - and no real signal that this is going to change - irrespective of the fact no doubt that the models will try and prematurely break it down

Yes it's not bad really is it it! We should see north sea temperatures continue to drop though over the next 10 days which eventually is going to aid us in keeping the jet south (even if we keep the Western -NAO) - and I notice GP is thinking the blocking should focus further East in 10 days or so - so our turn for a blizzard may still come. It would have been nice to get the snowfall while I'm on my hols though and don't have to drive to work!

Edited December 29, 2009 by beng

[azores92]

possibly SA, but would the irish sea not moderate the temperature in any easterly flow making the snow showers marginal? thursday in the day could possibly give some wintry showers to eastern coasts of ireland, but i cant see the showers penetrating too far inland. if the showers arent supposed to penetrate too far inland across the UK, i cant see them making too much inroads across ireland.

[Methuselah]

Yes that is a correct analysis, it did look like the Greenland High would extend far enough east towards Iceland, as well as linking up with heights towards the Siberian arctic in terms of sustaining an easterly or north easterly airstream for longer. Indeed there were promising signals on some of the modelling up to last night that this would happen. These spoiling shortwaves that keep tracking down from the north were a feature of the last cold spell and scuppered longer term snow potential for this part of the UK. As you say, the whole pattern is too west based in that respect and will keep favouring north western parts of the UK rather than southern eastern areas - with a tendency for troughs to pull the winds round to the north west or even west on the southern flank of the low pressure.

However, the overall picture certainly remains a cold dominated one - and no real signal that this is going to change - irrespective of the fact no doubt that the models will try and prematurely break it down

Good call, Tamara.

Surprising as it may seem , I find these shortwaves quite promising. Not just because the one-in-question might give me a right dumping - but because, should one evolve in the right place (southern North Sea?) at some point - parts of Eastern England could also end-up with a pasting??

I'm not sure quite when it was (early to mid 60s sometime - The Avengers (Emma Peel )was on TV! ) a NE snow shower-bearing wind being cut-off by a low from the NE. I think it left MK with 24-48hrs of snowfall...

I guess what I'm saying (re the models) is - don't panic! Once the cold air established - your time will come!

[snowmadchrisuk]

Surely the main thing is to get this cold to v.cold air really entrenched, then any bouts of PPN should make things interesting

If we can get them -10 850's over the UK for more than a few days , then any low coming up from the South would be very Interesting. The 6z is Just a peach of a run all the way through IMO.

[TEITS]

Im not sure I agree with some of the posts suggesting the block sinking SE in F.I. if you notice with the GFS its always in low res mode that this trend is suggested. At the moment im favouring the GEM ensemble mean which has been very consistent recently.

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

As for the E,ly being shortlived then to me its no surprise as this has been the trend for many days now. The simple reason for the E,ly is due to the S,ly tracking LP so it stands to reason this is shortlived as it transfers E.

Finally onto the ECM ensembles. Due to the mean being so low I would be utterly amazed if the mean didn't rise. However note at +240 the mean is at 0C. However I bet in a few days the mean for the +192 period is lower than currently suggested.

I see no reason why this cold spell will come to an end at the moment. The block may transfer W and bring us a W based NAO but to be honest the models are slowly backtracking from this especially the GEM.

Finally lets remember that this current cold spell only appeared at +168. Also according to the GFS before Xmas the New Year would be relatively mild. This isn't going to be a winter where the cold spells are modelled in F.I. At the moment I wouldn't go any further than +168!

[Guest North Sea Snow Convection]

I guess what I'm saying (re the models) is - don't panic! Once the cold air established - your time will come!

Certainly no panic at all.

Whatever criticisms of the GFS there have been (me amongst them) the GFS 06z is onboard with a persistent chilly theme. Patience is always a help - it looks perhaps that the shorter term prospects (the rest of this week) may have been put a bit of a hold, relatively speaking in terms of the colder easterly evolution, but the medium term is getting better and better

Edited December 29, 2009 by North Sea Snow Convection

[Snowaddict]

possibly SA, but would the irish sea not moderate the temperature in any easterly flow making the snow showers marginal? thursday in the day could possibly give some wintry showers to eastern coasts of ireland, but i cant see the showers penetrating too far inland. if the showers arent supposed to penetrate too far inland across the UK, i cant see them making too much inroads across ireland.

Pressure will be lower on Thursday in Ireland AZ92, Winds will be stronger to an extent..

From experience they penetrate on average up to 75 miles inland, which is very good in terms of Ireland.

You could be right but I'm very conifdent of seeing considerable inland penetration later on Thursday into Friday in Ireland, winds will be stronger and mroe direct here for a time.

EDIT: Any takers for NOGAPS @ T+144?

http://www.meteociel...&mode=0&carte=0

Also, exceptional GEFS Ensembles - Stunning really.

SA

Edited December 29, 2009 by Snowaddict

[Guest North Sea Snow Convection]

As for the E,ly being shortlived then to me its no surprise as this has been the trend for many days now. The simple reason for the E,ly is due to the S,ly tracking LP so it stands to reason this is shortlived as it transfers E.

The shortwave to the north was not modelled until now to develop the way it is, and therefore there was a good chance that the easterly flow coming off the back of the low pressure might be sustained for a longer period of time to bring ever colder upper air in from north east europe. Both the ECM and GEM (especially) consistently modelled this. However, it may be that the interruption is brief. There are signs that some of this colder air may still arrive after the weekend - but more output required to confirm this

[DaBrigg]

apart from Scotland

no really deep penetrating cold on the way

I noticed a number of posters dismissing you, but I have to say I agree from a local perspective. The Irish Sea is too warm.

Im on the coast also, and Ive seen rain here with 850hPa temps sub -10C, and thicknesses sub 520. Go a few miles inland and its all snow, but along the coast, forget it!

We will do better temp-wise later in the week, once we loose the easterly.

Unfortunately, we will then also loose the showers.

However it is an amazing weather pattern and long may it continue!

Have a look at some charts from around Jan 2008, for a reminder of what winter used to be like.

[Yeti]

Great models again this morning - however the trend has definitely moved away from the Siberian link up allowing the really cold, unstable air to reach the UK. Instead the block looks set to extend SEwards, sending the coldest upper air into central Europe while the UK sits in stagnant cold which, coupled with fallen snow, could create some very low minima:

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

This is a chart that caught my eye:

http://www.wetterzentrale.de/pics/Rmgfs1444.gif

I'm sure that would be record breaking cold for northern Germany and we can see why the De Bilt ensembles are forecast to crash!

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

Then once again the block looks like it may retreat westwards, allowing Arctic lows to push S. This would likely bring more moist but perhaps slightly less cold air, away from the North.

All in all, plenty of cause for excitement as this long cold spell returns to northern and central Europe (or is refreshed in the case of Scotland).

Edited December 29, 2009 by Yeti

[Tuxedo]

just a thought i've been pondering and welcome thoughts but do you think if this current set up with GH block and a southerly tracking jet stream occured 10 years ago it would have resulted in blizzards across the areas today that are proving marginal and producing sleet at the best. So in other words our UK climate has warmed by a degree or so in the last decade that now make the current set ups marginal while in the past they would have produced dead cert snow.

Anyway I've opened the freezer door to try and help bring the temps down to turn this wretched rain to snow!!!

[TEITS]

The shortwave to the north was not modelled until now to develop the way it is, and therefore there was a good chance that the easterly flow coming off the back of the low pressure might be sustained for a longer period of time to bring ever colder upper air in from north east europe. Both the ECM and GEM (especially) consistently modelled this. However, it may be that the interruption is brief. There are signs that some of this colder air may still arrive after the weekend - but more output required to confirm this

If I was honest Tamara I always thought this SW would be a pain which is why I said last night the window of opportunity is small. I still think Friday holds alot of convective potential and who knows we still might see some changes between +72 & +96.

Personally I would love a 1050mb Scandi HP with -15C upper temps being blown in on a strong E,ly. However we might have to wait for this.

[Guest North Sea Snow Convection]

just a thought i've been pondering and welcome thoughts but do you think if this current set up with GH block and a southerly tracking jet stream occured 10 years ago it would have resulted in blizzards across the areas today that are proving marginal and producing sleet at the best. So in other words our UK climate has warmed by a degree or so in the last decade that now make the current set ups marginal while in the past they would have produced dead cert snow.

Anyway I've opened the freezer door to try and help bring the temps down to turn this wretched rain to snow!!!

No, a pattern that is west based like this would produce the same. As Yeti has just correctly described, without pressure being high to the north east to advect the coldest air south westwards, in any historical situation the coldest air would always stay to the east of us and southern and south western areas of the UK particularly (therefore including your own) will and would always be too close to the atlantic milder battlegrounds. Hence the rain that are trying to change to snow via your freezer

Edited December 29, 2009 by North Sea Snow Convection