Winter Model Discussion 12Z 22/1/13 onwards.

[Gibby]

Good evening. Here is the evening look at the latest 12z output from GFS, UKMO and ECM for today Sunday January 27th 2013.

All models show an unsettled and windy week to come with today's showery Westerly flow backing SW tonight and tomorrow with a further spell of rain moving NE across the UK with renewed gales in the North and West. Tuesday too sees a lot of wind and rain over the UK with some very mild air for a time likely in the South through the day. Wednesday sees the potential for some damaging winds over Northern Scotland while the rest of the UK sees a rather chillier spell both Wednesday and Thursday with showers and bright intervals. By Friday a new Low pressure looks like crossing more Southern areas with rain and strong winds once more followed by a chilly interlude with more wintry showery conditions and the chance of night frosts over the weekend.

GFS then continues to show High pressure down to the SW with a succession of Low pressure areas slipping SE to the NE bringing several spells of rain followed by rather cold and windy NW winds with wintry showers, especially towards the North and East. signs of a more substantially cold Northerly look likely following the last chart of FI.

The GFS Ensembles show a trend towards chillier conditions as we progress through the run though nothing more than average conditions for more Northern locations. Rain though does decrease in quantity the deeper into the run we travel especially in more Southern locations.

The Jet Stream continues tunnelling over the Atlantic towards the UK for the majority of the coming week. It then rides over the Azores High and travels back South just to the East of the UK next weekend and beyond. If cold air is to reach the UK in a meaningful way we need this High pressure to weaken and absorb North to Northern latitudes so that the Jet Stream becomes forced further and further South as it was in the recent cold spell, a process that doesn't look likely in the short term.

UKMO for midday on Saturday shows a ridge of High pressure collapsing SE over the UK with a fair day for many in rather colder temperatures than those of the days previous. It looks as though milder Atlantic winds will spread back over the UK the following day.

ECM also shows the collapsing ridge over the UK next Saturday before it too shows the Atlantic winning back late in the weekend with rain returning from the West. With time though the rain bearing fronts and depressions slip further SE into Europe with the Azores High extending further North through the Atlantic and in response to the Atlantic weakening allows for impending and increasingly cold weather in the days beyond Day 10.

In Summary tonight the weather looks like staying Atlantic dominated for the foreseeable future. The biggest enemy for cold weather fans from tonight's run is the strong Jet Stream riding over the Azores High which is displaced slightly North or Northeast of it's home base at times. As long as that positioning is maintained any cold incursions will be just that with the Atlantic riding over the top of the High courtesy of the Jet flow then delivering the cold zonal flavour to the weather for our European partners rather than the UK. ECM shows what can happen if that High is allowed to ridge North in response in part to a weakening of the Atlantic and Low pressure finding it's way down to the Med.

[Isolated Frost]

Not quite full retrogression on the EC suite- but as touted previously, a lot of mid-atlantic highs being spawned off the Eastern Seaboard- and the stalling, amplified trough to the west at 240 is bingo..

Advancing cold pool and -ve anomaly set in place for C Europe, here we go !

[bluearmy]

Ecm has not wanted to drop heights north of greenland. As such, all the ridges are transient thus far. We need to see evidence of cross model agreement for heights in the greenland area to be conducive to a real greeny block or we shouldn't expect one. There is no requirement for one to provide us with proper cold anyway. I dont think we will see one before the 10th anyway. Funnily enough, the ecm op at day 10 does look like providing a fair pump of waa towards w greenland but a day 10 op is of little value. The nw/se movement of shortwaves seems the current favourite and then its all about timing.if we see a ridge thrown north at the same time as the arctic ridge is in the right place then you may well see the support required to get a cuut off greeny block. Would like to see the pattern a bit further west so the shortwaves diving se could avoid bringing their pm warm sectors across the entire uk

[damianslaw]

Models continue to move towards a colder theme as we move through February proper, showing a increasingly amplified atlantic flow and a more west based Canadian vortex which in turn will aid warm air advection over the western side of Greenland which is key if we are to see heights building strongly over Greenland and a link up with the mid atlantic heights.

ECM and GFS this evening both show the azores high not getting in on the act either. The result low pressure and trough moving down across scandi and heights increasing to our NW in time.

In the meantime the current milder spell does now look a relatively short lived affair, northern parts will be back to average by Thursday, and Friday and Saturday look preety chilly with wintry showers and the return of air frosts. There does appear to be much less energy in the atlantic than was being suggested a few days ago, we were forecasted gales last night a few days ago, alas we hardly had a breath of wind, and Tuesdays low pressure system now looks a much tamer affair. It indicates the energy spilling out of the canadian vortex is not particularly potent again evidence the canadian vortex is weakening considerably - remember it is normal for the PV in general to weaken as we move through February, this in itself increases the chances of northern blocking occuring much more so than in December and January.

[Jason T]

I wouldn't go patting yourself on the back just yet...

I go along with your prediction of some more sustained cold weather as we head into February but it is not nailed on yet.

Care to elaborate.?. I believe it was always stated prior to the last event beginning,That we would see a Brief Mild spell before the full effect of the SSW delivers into early Feb.

[Jason H]

. Would like to see the pattern a bit further west so the shortwaves diving se could avoid bringing their pm warm sectors across the entire uk

I agree with your sentiment. I am sure that in time we'll see corrections Westwards. Still early days with regards the exact patterns, although it does seem to be heading down a colder route.

[ANYWEATHER]

To be honest its amazing how the models just a day or so ago were predicting a prolonged spell of mild weather, now there predicticting something much colder! No charts to verify but some interesting times ahead....

[ScottSnow]

Care to elaborate.?. I believe it was always stated prior to the last event beginning,That we would see a Brief Mild spell before the full effect of the SSW delivers into early Feb.

Elaborate on what ?

I can certainly see the potential for colder weather as we head into Feb and agree broadly with TEITS assessment however it is too early at this stage to say this is definitely going to happen.

[J10]

Good evening. Here is the evening look at the latest 12z output from GFS, UKMO and ECM for today Sunday January 27th 2013.

All models show an unsettled and windy week to come with today's showery Westerly flow backing SW tonight and tomorrow with a further spell of rain moving NE across the UK with renewed gales in the North and West. Tuesday too sees a lot of wind and rain over the UK with some very mild air for a time likely in the South through the day. Wednesday sees the potential for some damaging winds over Northern Scotland while the rest of the UK sees a rather chillier spell both Wednesday and Thursday with showers and bright intervals. By Friday a new Low pressure looks like crossing more Southern areas with rain and strong winds once more followed by a chilly interlude with more wintry showery conditions and the chance of night frosts over the weekend.

GFS then continues to show High pressure down to the SW with a succession of Low pressure areas slipping SE to the NE bringing several spells of rain followed by rather cold and windy NW winds with wintry showers, especially towards the North and East. signs of a more substantially cold Northerly look likely following the last chart of FI.

The GFS Ensembles show a trend towards chillier conditions as we progress through the run though nothing more than average conditions for more Northern locations. Rain though does decrease in quantity the deeper into the run we travel especially in more Southern locations

Apologies for part quote, not to take up too much room.

Good analysis as ever, however if the GFS came off as shown, which is a massive big if, I would expect Western areas to get a fair few wintry showers at times.

Edited January 27, 2013 by Jackone

[Froze were the Days]

Even if we do get displaced heights from the Azores Hp further west and height rises then to the North East I still don't think we'll see the PV near Greenland go anywhere so I suspect any height rises to the North East will be 'under pressure' from the Atlantic almost as soon as we experience them. Still see no signs at all of heights in the Greenland area which has been apparent throughout this winter.

[Grimsby Snow Lover]

Elaborate on what ?

I can certainly see the potential for colder weather as we head into Feb and agree broadly with TEITS assessment however it is too early at this stage to say this is definitely going to happen.

I agree with what you have said here as there are no guarantees predicting weather, especially after 4 days. The TRENDS do remain positive for a colder outlook after this week though at present which is enough to keep me and no doubt many others interested in the models over the next week or so.

Edited January 27, 2013 by Grimsby Snow Lover

[shotski]

Even if we do get displaced heights from the Azores Hp further west and height rises then to the North East I still don't think we'll see the PV near Greenland go anywhere so I suspect any height rises to the North East will be 'under pressure' from the Atlantic almost as soon as we experience them. Still see no signs at all of heights in the Greenland area which has been apparent throughout this winter.

But they can and will exist together side by side. Take Feb 1947 as an example, split polar vortex with most of the energy over

northern Canada.

[BLAST FROM THE PAST]

I'm thinking here that maybe we may not see much movement of the PV over Canada but we 'll see it either weaken and lose its influence as retrograde motion comes into play and the split will be more pronounced with Siberian sector being dominant and the Canadian sector being weaker and further 'west', or if it does moves it will move over the pole to Siberia. As a result we'll see the Atlantic block up. This in turn will allow or be part of the retrograde motion from our east with HP building to our E/NE. So in short I think if our cold pattern emerges then it won't start through a GHP but that will develop on from Russian to Scandi HP retogressing. I smell 1986. Having said that....I don't really care how it develops, as long as it does

BFTP

Edited January 27, 2013 by BLAST FROM THE PAST

[Jaffusmaximus]

I'm thinking here that maybe we may not see much movement of the PV over Canada but we 'll see it either weaken and lose its influence as retrograde motion comes into play and the split will be more pronounced with Siberian sector being dominant and the Canadian sector being weaker and further 'west', or if it does moves it will move over the pole to Siberia. As a result we'll see the Atlantic block up. This in turn will allow or be part of the retrograde motion from our east with HP building to our E/NE. So in short I think if our cold pattern emerges then it won't start through a GHP but that will develop on from Scandi HP retogressing. I smell 1986. Having said that....I don't really care how it develops, as long as it does

BFTP

Hope you do not mind me adding some snapshots from 86 to illustrate what a difference 10 days made!

for comparison

transformed into

I have been out of interest going over Jan/Feb 86 and its an uncanny the resemblance with the current model output!

Edited January 27, 2013 by Jaffusmaximus

[BLAST FROM THE PAST]

I have been out of interest going over Jan/Feb 86 and its an uncanny the resemblance with the current model output!

Jaffus

Indeed it is.....and a classic 'descending' winter

BFTP

Edited January 27, 2013 by BLAST FROM THE PAST

[Long haul to mild]

Indeed, lots of examples of the dreaded AZH mid Atlantic blob and the odd temporary ridge but full on Greenland highs are rather thin on the ground. If its coming it will be via a Scandinavia high / ridge. Greenland high will happen though, we just need to wait until late April.

Jason

Oh yes, a GH is absolutely nailed on to be there from late April to early September, so another cricket season gets ruined!

I think it is fascinating to see how, in just a space of two or three days, the models have dropped their idea of strong W or SW winds with heights over S Europe and are now much more in favour of a mid Atlantic ridge. Given this change at short notice, perhaps the next stage is to move the heights even further NW towards Greenland, preferably well before April!!

[chionomaniac]

I think perhaps you need to be able to distinguish the difference between a 'true' greenland high & some transient ridging into Greenland-

The GFS has not developed a greenland high in any model except the odd 18z flirtation at 360.

You are of course trying to blend the models to your forecast, but it reality there are ZERO greenland highs being modelled so you current assessment is a little wide of the mark-

The GFS tends to perform well in Northerly topplers, infact I recall December when I used the DAY 10 GFS 12z to forecast an outcome when did land very close.

Also when the prospects are there for a proper GH the GFS tends to model that very well with vertical advection from a Neg tilted high well west of Greenland-

What we have here is a positive tilted low when will overun the pattern- there is of course 2 ways 2 cold from the east from this evolution- one from a genuine GH looks out of the question, not just because of its absence in the models but also from its total absence this Winter-

THe other evolution is the low 'toppling' reaches greenland & a chunk of energy dives south drawing some high pressure towards Svalbard where eventually you get undercutting-

Again as rare as hens teeth.....

I would say people need to sit tight, proper cold ( thats away from a quick northerly toppler) is still 8-10 days +++

S

as roy walker used to comment: Say what you see....

I think that currently this is a fair reflection of what is expected in the 10 day time frame. Only time will tell whether an amplified Azores ridge will grow into a stronger Greenland block with undercutting.

Overall we are seeing some more alignment of the MJO pattern with the forecast anomaly pattern around day 10.

http://www.cpc.ncep....clivar_wh.shtml

The average MJO forecasts take us into phase 8 at the start of February - the expected H500 anomaly here is for a northerly displaced Azores ridge and west based -ve NAO.

No true GH is forecast here but we may not need it to still get cold sourced directly over the UK. In fact the only Feb MJO H5 anomaly that showed greater raised heights in Feb is phase 3 (ECM takes us there in the extended range)

There is a lot of support for the amplified Azores ridge from the ensemble anomaly charts - both the GFS and ECM

So we will be positioned on the cold side of an Atlantic ridge as we enter Feb.

This is supported by the lower strat charts as well as can be seen from the 100hPa chart at day 10

So a cool/cold start to February with the chance of a greater northern blocking once the pattern becomes established especially if the Pacific ridge can wane allowing the Greenland ridge to develop more.

[london-snow]

Okay so based on my previous thoughts here is my punt on the way forward :

28th - 2nd : A much milder week ahead however with showers or longer spells of rain during this period. As we move into the weekend i am looking at the atlantic to become cut off and introduce a more settled period of weather where frosty weather will take hold through much of the uk and temps to take a drop to just below average.

3rd - 7th : After a dry start i am looking at a much more colder & wintry pattern to take control from the north.

Beyond this period or just a tad before i am looking at the northerly to tranfer to north east ~ east and become locked in for some time.

That's my view & punt so don't take for gospel. Good times ahead i feel.

[Summer Sun]

ECM ensemble

There is certainly a cluster trending colder but many more runs are needed yet I feel before we can be certain of a cold spell

[Polar Maritime]

Okay so based on my previous thoughts here is my punt on the way forward :

28th - 2nd : A much milder week ahead however with showers or longer spells of rain during this period. As we move into the weekend i am looking at the atlantic to become cut off and introduce a more settled period of weather where frosty weather will take hold through much of the uk and temps to take a drop to just below average.

3rd - 7th : After a dry start i am looking at a much more colder & wintry pattern to take control from the north.

Beyond this period or just a tad before i am looking at the northerly to tranfer to north east ~ east and become locked in for some time.

That's my view & punt so don't take for gospel. Good times ahead i feel.

Any models to back this up ?

[Summer Sun]

The ECM ensemble run now agrees on a brief rise in pressure later this week

By Monday the HP gets pushed south

ECM's ensemble run ends with high pressure just to our south west with 1020mb lines just edging into the south west, parts of Ireland and wales

[sixfootdrifter]

Any models to back this up ?

Normally a lurker but felt compelled to make a small post.

The forecast is his own and not based on the models. Lets face it the models are only a computers mechanical thoughts so to speak.

This is only my observation and i have no desire to ruffle the feathers of people who are far more knowledgeable than myself. Anyone that puts themselves in the firing line has my upmost respect.

Edited January 27, 2013 by sixfootdrifter

[london-snow]

Any models to back this up ?

Yes plenty of support for this to happen up to the northerly as stated.

After that period it is a punt as stated but not a wild guess.

- Jet going south.

- Blocking to become established.

- SSW Effects to take effect.

I have said it is a punt and a punt it will remain even if it comes off as planned. I am not a forecaster & nor are you however we both have intrest in the weather the diffrence being i am trying to read between the lines and make a punt where as you are just reading the models into fi which has just as much of a chance of coming up as my forecast coming up.

Whatever will be will be & time will tell.

Edited January 27, 2013 by london-snow

[Catacol]

I'm thinking here that maybe we may not see much movement of the PV over Canada but we 'll see it either weaken and lose its influence as retrograde motion comes into play and the split will be more pronounced with Siberian sector being dominant and the Canadian sector being weaker and further 'west', or if it does moves it will move over the pole to Siberia. As a result we'll see the Atlantic block up.

BFTP

Well - this has been oft-repeated this winter but yet to happen. If it doesnt happen at least once before Spring comes then there will be a lot of post-facto analysis as to where it all went wrong. The vortex love affair with Canada is so pronounced this season I'm wondering whether I should take a holiday there myself... Must be something about the place.

[Grimsby Snow Lover]

Another positive tweet from fellow member Matt Hugo regarding possibilities after this weekend.

Matthew Hugoâ€@MattHugo81

Reviewed and definite trend/signal in the EC ENS for more of a N or NW'ly flow after first week of Feb as blocking re-develops.