Winter Model Discussion - Cold Hunting - 20th Dec

[cooling climate]

It is now obvious I think that the higher pressure that we are now seeing being modeled to

the south aiding in the zonal flow across the UK is why the Meto changed their cold outlook

several days ago. All the other long range guidence changed at the same time and it has

been nagging me until now as to why.

The default pattern now it seems for the next several weeks is for a zonal flow compared to a

couple of weeks ago where they thought there would be more in the way of northerly type airflows

and colder weather. This pattern change could very well be to do with a descending positive QBO

and westerly winds at 50-60 degree latitude hence the higher pressure futher south.

All is not lost though for winter weather lovers as a more active MJO, strat warmings and strong

mountain torques can all be big pattern changers.

As far what the models are showing at the present time I think the warming that is about to start at

the 30mb level has more to offer than what the models are presently showing and I am hopeful

that future runs will show stronger heights developing to our north and northwest which should

help to steer the jet further south as well.

The warming is a bottom up warming so should have some impact straight away and then

towards the end of the year the top down warming which has been showing up in the models

for some time will begin although this will have a lag effect and of course does not offer a

definate cold solution for the UK but our chances of cold have to be a lot greater I would have

thought.

[nick sussex]

This is what NOAA refer to as a canonical negative AO pattern, its as close as I could find to that anomaly in the research paper, I've yet to work out how to copy and paste from a PDF file, if there is indeed a way!

But I think what they're alluding to is that the current negative AO is not really typical of the anomalies you'd find in their estimation on past history. So here it is!

[shotski]

It is now obvious I think that the higher pressure that we are now seeing being modeled to

the south aiding in the zonal flow across the UK is why the Meto changed their cold outlook

several days ago. All the other long range guidence changed at the same time and it has

been nagging me until now as to why.

The default pattern now it seems for the next several weeks is for a zonal flow compared to a

couple of weeks ago where they thought there would be more in the way of northerly type airflows

and colder weather. This pattern change could very well be to do with a descending positive QBO

and westerly winds at 50-60 degree latitude hence the higher pressure futher south.

All is not lost though for winter weather lovers as a more active MJO, strat warmings and strong

mountain torques can all be big pattern changers.

As far what the models are showing at the present time I think the warming that is about to start at

the 30mb level has more to offer than what the models are presently showing and I am hopeful

that future runs will show stronger heights developing to our north and northwest which should

help to steer the jet further south as well.

The warming is a bottom up warming so should have some impact straight away and then

towards the end of the year the top down warming which has been showing up in the models

for some time will begin although this will have a lag effect and of course does not offer a

definate cold solution for the UK but our chances of cold have to be a lot greater I would have

thought.

Hi all

Is the forecast ssw for the beggining of Jan actually being fed into the raw data of ECM, GFS etc or are the charts

we are currently seeing not taking into account any potential ssw ?

[A Winter's Tale]

Good evening. We've seen many problems with flooding across many areas today. Tonight, this band of heavy rain and persistent rain should slowly move northeastwards bringing further rainfall to eastern parts of England and Scotland with blizzard conditions in the Grampian highlands (as low as 500-600m) and the strong southeasterly wind could bring some coastal flooding issues to some spots along the north sea coastline of Scotland. Ireland should br largely dry tonight, so too Wales and southern and western areas of England with some clear spells towards the south. There could be further wild conditions for the Shetland Islands with the strong south easterly winds causing problems in the north sea and the uppers here are possibly low enough for wintry precipitation. Tonight's minima should be 4 to 8C.

Friday morning should see drier conditions slowly spreading from the south west with much of precipitation in north eastern Scotland. Certainly a risk of flooding in Aberdeenshire and it's important to note that the discarge of the rivers oftern reach their highest peak after the rainfall. And of course hill walking in the Grampians will be an extreme affair tomorrow with a mixture of snow, strong winds. In the very southern parts of the British Isles, however, there could be some sunshine with the first daylight of the winter solstice.

During the afternoon there could still be further rainfall in north eastern Scotland but hopefully it should be turning lighter here before it clears into the north sea. Some sunny spells in a few areas of England and Wales before sunset and indeed before the next area of rainfall. Maximum temperatures of 5 to 9C.

For Friday night - if we are still here of course - another area of heavy and persistent rain should arrive from the south west. Across more central and eastern parts of England there could be some clear night skies before being pushed eastwards as rain makes further progress. There may even still be some light rain or drizzle for north eastern Scotland. Minimum temperatures of 3 to 6C.

For Saturday it's looking like a very wet affair for many with further heavy and prolonged rainfall increasing the risks of flooding. For England and Wales it should be pretty mild - however in Scotland there could be a combination of rainfall and temperatures of around 6C aswell as a strong southerly wind. Overall highs should range from 5C in highland Scotland to 15C in the very south of England.

And Sunday night is also looking wet too with the rain band over Scotland and other features moving into the south west and ontop of that quite strong winds too. But it will be mild in England and Wales, lows across the British Isles ranging from 2C in Shetland to 12C in Cornwall.

For Sunday, the rainfall should be situated over across Scotland whilst elsewhere - other than some light rain in Ireland - it could be drier with some sunshine in southern areas. Mild too with highs of 8 to 13C.

For Sunday night, rain should persist across parts of Scotland whilst another system knocks on the door of southern England. A mostly overcast night and quite mild with lows of 5 to 9C.

For Christmas Eve, the low of 972mb is centred to the north of Scotland, thus, further rainfall for northern Scotland should be extended and there could be further persistent and fairly heavy rainfall across Wales, southern and central parts of England. Drier for northern England into southern Scotland aswell as Ireland. Maximum temperatures of 6 to 11C.

For Christmas night, it could be a little colder as winds turn to more of a northwesterly and there could even be some wintry precipitation for northwestern areas. Lows of 2 to 7C. There could be light rain for parts of Scotland and showers across western and possibly southern areas in a cloudy night for most.

For Christmas Day, there's certainly much more of a chance of a white christmas this year compared to last year but we'll only know at the time of verification. However, it seems that a cold northwesterly flow should continue throughout Christmas day with low pressure centred close to the Shetlands - feeding showers in northwestern areas and these could be wintry, particulary on the high ground but further into the day, judging on recent charts snow could be falling to lower levels so don't rule out an official white Christmas in Belfast or Glasgow. A cold day perhaps with below average maxima in northern areas - possible highs of 2 to 8C.

There is the potential for the risk of snow showers to increase overnight into the early hours of Boxing Day in what looks like quite a potent northwesterly flow. Certainly if this verifies, it would be perfectlty festive weather.

Confidence is low beyond Christmas as details will change but there is a consenus for a cold, changeable, showery and a seasonal end to December and to 2012. Certainly, I'd say that Scotland and possibly Northern Ireland and northern England are favourable for a cold period following Christmas, possibly cooler than of late in the south but depending on the positioning of depressions, it could be milder here under the warm sector. So certainly very much to look out for regarding the final third of December, potentially we could see an example such as late December 2000 or 2001 with a colder theme between Christmas and the New Year.

For fun, the GFS 12z was interesting, certainly from a Scottish perspective as we near Hogmanay.

Frontal snowfall later on Boxing Day

A return to a cold, fresh and quite potent northwesterly flow for the 27th

Another frontal snowfall for the 28th

Followed by a reload on the 29th

An interesting Hogmanay - scarfs and gloves required.

And a breakdown by the 2nd of January

Anyway, in the meantime we've got some wild and active weather in the run-up to Christmas with further concerns regarding flooding.

[Tim Bland]

Does anyone know if different upper air temperatures required for snow vary between countries / continents? I have always assumed -5c uppers and 0c dew points are required regardless. Looking at the GFS precip types for the next week it often shows snow over mainland Europe with -2c uppers whilst the same air over the UK produces rain. I know a massive factor is elevation but I am talking about locations away from the alps etc. is it because of natural cooling over land etc? any answers wold be most appreciated.

[JP1972]

Does anyone know if different upper air temperatures required for snow vary between countries / continents? I have always assumed -5c uppers and 0c dew points are required regardless. Looking at the GFS precip types for the next week it often shows snow over mainland Europe with -2c uppers whilst the same air over the UK produces rain. I know a massive factor is elevation but I am talking about locations away from the alps etc. is it because of natural cooling over land etc? any answers wold be most appreciated.

Is it not because we're surrounded by water and whichever angle a weather front comes at us from the air within is modified by crossing water?

[Bobby]

The NMM shows a lot of rain to come on Saturday, 100mm for my house in around 24 hours cor blimey. If that falls onto the already flooded ground then it could be pretty disastrous, rain looks fairly intense too.

Edited December 20, 2012 by Bobby

[Zenarcher]

Model summary using the GFS, ECM, UKMO, GEM, NOGAPS and JMA.

48 hours Saturday - We still have the models unsure on the low that will bring very wet weather and windy conditions this weekend most agree on something like this,

For the wind if the low is deeper and the Russian high pushes in more it will be more windy across the Northern parts of the country this is what varies between the models but they all agree on windy weather. What they can agree on is for very heavy and long lasting rain over the weekend as the GFS below shows,

Saturday Rain being very widespread across the whole UK,

72 hours Sunday - All models show a low around 975mb over the North of Scotland the GEM model is the only one that doesn't and places the low way out in the Atlantic. We see the models agree on very strong winds over the far North of Scotland average wind speeds there over 55mph, They also agree on the rain staying with us through Sunday as well,

96 hours Christmas Eve - The models agree on the low from Sunday starts to weaken and with it so does the wind but rain still stays around,

120 hours Christmas Day - All models show something along the lines of high pressure to the West of Greenland and low pressure to the East of Greenland this set up would give us a cold Northerly to North Westerly wind, the GFS shows cold minimum temperatures,

As for snow it's difficult to predict that even at short range so what the models currently show will change, the ECM snowfall maps restrict it to the Scottish Highlands and the GFS gives us some wintry weather across Northern parts of the UK.

144 hours Boxing Day - All models still show high pressure to the West of Greenland and low pressure to it's East as for the UK it heads into unsettled weather with some Atlantic lows moving in.

Overall - Models are still undecided on the low expected in 48 hours time but they all agree on a unsettled picture to end the week with plenty of rain and wind for much of the time, flooding is the main concern. After this the models show the low from the weekend weakening and later through the Christmas period they show a cold N to NW wind that I expect will give us cold temperatures but for where any wintry weather may fall is tricky to say at the moment. After the Christmas period the models show the Atlantic weather move in more and giving us a unsettled spell to end the month. GP today did say in the strat thread that he still believes warming to take place around the 7th/8th of January.

[Cloud 10]

Wintry showers into the North of Scotland first thing on Christmas morning

from the 18z.

[SnowObsessor90]

Wintry showers into the North of Scotland first thing on Christmas morning

from the 18z.

Phew, someones finally posted, I actually thought the world may have started to end early for a minute then.

[Panayiotis]

More improvements compared to the 12z for the big day first note, Azores high further south on this run, 2nd note we have more of a northerly bringing us the colder uppers faster!

Edited December 20, 2012 by Panayiotis

[swfc]

Nipped on here expecting delerium or despair ?bit of a know mans land really.Outlook--windy and unsettled with heavy rain mixed in with showery periods.Average to cool with the odd chance of some wintry showers over xmas period.I think after recent events any talk of strat warming events should be left where they belong in fi.Wait while something shows up in the output -models ete.

[bryan629]

looks like an upgrade so far, gh pushing the low at 138hr a bit further south

[nick sussex]

I just wonder whether that next low moving in could take a more se track a touch further west.

Something to look out for in the ensembles later, this could provide a bit of interest on its northern and ne flank.

Edited December 20, 2012 by nick sussex

[swfc]

looks like an upgrade so far, gh pushing the low at 138hr a bit further south

There really is no true greenland high on that chart,its a surface feature

[Weathizard]

Perhaps its IMBYism in a way but I cant really get excited about some of the charts we are seeing, disgusting wet muck for us southerners and its really NOT what we need, right at this time give me a dominant high pressure over us any day of the week. Just need a break from this now.

[Panayiotis]

There really is no true greenland high on that chart,its a surface feature

It doesn't matter a surface high can still act like a wall and deflect lows, however a proper Greenland high, that we are looking for is stronger than a surface high as these can be 'knocked' down easier incoming lows also a Greenland high helps stop the Atlantic from bombarding us from low pressure. Edited December 20, 2012 by Panayiotis

[Neiller22]

Cannot believe how quiet this thread is with the potential in the outputs for the northwest!! Could be a white Xmas for some. If this was showing as the beast from the east this forum would be in meltdown!!! It's unreal. Unless its the beast from the east nobody is interested !! Surely it's a forum for the whole of the uk to talk about the weather

[Panayiotis]

Fi for me starts at 140hrs as the 18z and 12z take different routes, one with cold the other with warm, very much chalk and cheese, which one is right however, is anyone's guess.

Edited December 20, 2012 by Panayiotis

[swfc]

Perhaps its IMBYism in a way but I cant really get excited about some of the charts we are seeing, disgusting wet muck for us southerners and its really NOT what we need, right at this time give me a dominant high pressure over us any day of the week. Just need a break from this now.

There is nothing in them charts to get excited about in reality.Any sign of a small incursion of cold air and wintry showers is almost met by an orgasmic response by some!Understandable in a way but unsettled ,cool and very wet seems the way in all honesty

[peterf]

Cannot believe how quiet this thread is with the potential in the outputs for the northwest!! Could be a white Xmas for some. If this was showing as the beast from the east this forum would be in meltdown!!! It's unreal. Unless its the beast from the east nobody is interested !! Surely it's a forum for the whole of the uk to talk about the weather

some of us have been flat out for weeks now, and need a bit time out lol.,i'll start getting excited if it's still showing late Saturday.

[-uksnow-]

Could someone do me the honour of explaing 500hpa charts? Are they linked to inversions?

For example i know this will unlikely come off, but what do they mean?

[Cloud 10]

Looks like the polar vortex fancies a trip to Scotland for new year.

[Tim Bland]

Some serious snow fall for Scotland is possible next week. Also much if Scandinavia and out to our east will get plastered! How far south with that pv come!? At least it shows signs of backing west which leaves room for heights to raise over Greenland

http://www.meteociel.fr/modeles/gfse_cartes.php?ech=192&code=0&mode=0

[on the coast]

Wet cold and windy seems to be the fair for the next week or so. Looking forward to seeing the trends for early January.