Winter Model Discussion - The Hunt For Cold -18z 17/12/12

[phil nw.]

Let`s keep on topic please-Model Output.

There is a thread for Met.Outlooks as well as the other Winter threads.

Thanks.

[Fred Sykes]

Well as there is no hope of cold in the near future, I suppose heavy rain and flooding is the next exciting thing we can hope for.

[Zenarcher]

This evenings model summary and comparison using the GFS, ECM, UKMO, JMA, GEM and NOGAPS.

72 hours - Between all the models we have good cross model agreement with most things it's just really the Atlantic low or lows we have crossing over and heading towards the UK where the large differences are at this short time frame,

The UKMO, NOGAPS and JMA show a low around 980mb or 985mb crossing the Atlantic like this,

The GFS and GEM disagree and have two lows and they are much closer to the UK as well,

Then on it's own the ECM it's sort of in between, it places just one low where the GFS and GEM place it but it's just one low at a similar depth as the UKMO etc,

We have disagreements here where you wouldn't normally expect them everything else seems similar between them just the lows.

96 hours - Again all the models show a similar picture apart from the Atlantic low which is now expected to be either to the West of the UK or over the UK,

JMA, NOGAPS and GEM place a low to the West of the UK around 970mb,

Our three main models the UKMO, GFS and ECM place a low over the North West of the UK that's around a similar depth to what the other three suggest,

Whatever the outcome here the models do paint up a unsettled spell of weather.

120 hours - All the models apart from NOGAPS show something very similar here we have a weak low over the UK,

This is where things start getting interesting over Greenland and in the Northern Hemisphere we have pressure building there and we have PV pushing down the Eastern side of Greenland, of course exact details vary between the models but at this range it's expected the important thing is they all show a similar picture.

144 hours - It's Christmas day and not bad charts rolling out tonight for it, models agree on heights building into Greenland and a cold Christmas day the GFS gives minimum temperatures below 3c across much of the UK on Christmas morning. As with 120 hours and the same here there's no point getting down by any exact details shown here at this range the important thing is the models show this and are continuing to show it.

168 hours and beyond where big changes will happen - GFS does give PV a hard time here but seems to want to bring in the Atlantic weather for most of the time, ECM continues to keep the Greenland high going and makes the Atlantic weather weak, NOGAPS has high pressure over Canada and Greenland giving us a very blocked pattern and JMA keeps high pressure near Greenland and keeps the Atlantic weather away.

Overall - The models are still clearing struggling where you'd normally find them not to be, still big differences between the Atlantic lows but they all do agree on high pressure building in over Greenland at some point next week which could lead us to have a cold Northerly air come down in time for Christmas but at the moment it is good to see some consistent runs from them all now at this time range just a few days ago we never really saw anything like this but they seem to have picked up on something now that we are closer to the time.

[Captain Shortwave]

Have they changed that much? , apart from the odd run that predicted we may see some cold(er) weather over xmas,most of the models have been pretty consistent in my opinion ,pointing at a normal/average/wet run between now and the new year.

i would dearly love them to suddenly change to a cold/snowy outlook ,but i suspect that we will be well into January before that materializes

Maybe (I might be wrong there), but there has been a lot of differences in handling the Russian high over the past week, to be honest there have been cold and very mild runs though over the last 24 hours they seem to have settled of an average and unsettled pattern for the big day. After that it depends, for the run up to new years yet again we seem to be close to some very cold air, but we also have the signal for milder weather to push northeastwards. Small tweaks could put one of these in favour at least for a few days. Though unless things change on a broader scale, we are stuck in this pattern of rather average weather.

[Zakos]

There is no reason to throw in the towel for this possible northerly, just as there was no reason to get excited about an easterly earlier in the month

There was never a potent easterly shown within the reliable timeframe (96 hours)

Nothing shown in the reliable timeframe now disregards the prospect of a Northerly. IMO the reliable timeframe for northerlies is longer than that of easterlies. (for a number of reasons which I shall not go into)

Nevertheless, there is still ample time for change. It will not take much change to make things much more favourable for a cold spell.

We have this at 144 hours.

As opposed to this.

While the current forecast looks like a west based -NAO, the potential is there for a potent cold spell with a small change. We dont have a raging polar vortex or jet stream as we did last year.

Edited December 19, 2012 by Zakos

[Summer Sun]

Here's the latest from Ian Ferguson in the south west thread not good for the south west I'm afraid rain wise

Thanks, Paul, for opening this timely new thread. Some worrying prognoses in the model output as we head towards Christmas and for sure, the omnipresent threat of flooding will again top the headlines now and again in areas previously badly affected. A key concern for here and now is the broad comparison between events unfolding now into tomorrow with those of 20-21 Nov. Meanwhile, with very good EC and MOGREPS agreement,the unsettled S-W regime shows little hint of let-up barring a temporary colder, showery NW phase post-Christmas but with a return to a W'rly flow thereafter into the trend period out towards 15 days. Clearly, we'd want to see some relaxation of this into early Jan to allow some drying-up to take hold, but there's little hint of any major pattern change as things stand. Not good.

The rainfall totals are not good at all there's likely to be flooding and traffic chaos during the final weekend and big getaway for Christmas

By Christmas eve the totals get worse

The only places which escape the worst really is the south east corner and Ireland (republic & northern)

100mm in places by Christmas day

Even after Christmas it just gets worse with almost 112mm for some places

This is not going to be a happy Christmas for some that's for sure

The sooner the pattern changes and we get a prolonged dry period the better its really needed now those in the south west must be fed up now with all the rain this year

[PubliusEnigma]

One useful tip, if we look at T+0 thru to T+24 in particular at this evenings ECM. With continental south easterlies, we can see

from the current forecast what one could expect thru the remainder of the winter under a similar set up. thus ;-

A chart if seen out in FI or even within the reliable resembling the above is likely to result in copious rain and little if any snow

and only then above say 500m on the Scottish Mountains. There has been talk of blizzards resulting out of such a set up, over recent weeks. The bigger worry under a set up like this would be the high rainfall totals in the SW and parts of the west.

[492]

There is no reason to throw in the towel for this possible northerly, just as there was no reason to get excited about an easterly earlier in the month

There was never a potent easterly shown within the reliable timeframe (96 hours)

Nothing shown in the reliable timeframe now disregards the prospect of a Northerly. IMO the reliable timeframe for northerlies is longer than that of easterlies. (for a number of reasons which I shall not go into)

Nevertheless, there is still ample time for change. It will not take much change to make things much more favourable for a cold spell.

We have this at 144 hours.

As opposed to this.

While the current forecast looks like a west based -NAO, the potential is there for a potent cold spell with a small change. We dont have a raging polar vortex or jet stream as we did last year.

Although models now mostly agree on the evolution until T+72 it is still a knife edge situation close to the UK as very cold air currently feeding into Poland from Russia continues its journey westward over the next three day.

[Iceaxecrampon]

12Z

Upgrade for Pennines on the 27th - all maybe not lost - all eyes on the 18Z watching that northerly plunge.....

Ian

[Iceaxecrampon]

Here's the latest from Ian Ferguson in the south west thread not good for the south west I'm afraid rain wise

The rainfall totals are not good at all there's likely to be flooding and traffic chaos during the final weekend and big getaway for Christmas

By Christmas eve the totals get worse

The only places which escape the worst really is the south east corner and Ireland (republic & northern)

100mm in places by Christmas day

Even after Christmas it just gets worse with almost 112mm for some places

This is not going to be a happy Christmas for some that's for sure

The sooner the pattern changes and we get a prolonged dry period the better its really needed now those in the south west must be fed up now with all the rain this year

Worrying indeed - what became of the drought warnings of early 2012 for the South? - anyone forecast this? - no - I thought not.......

[damianslaw]

Unlike recent days, there is more consistency between the models this evening with regard to the 72hr-144hr timeframe, all are now in agreement that the russian high will be forced to move eastwards thanks to changes in the upstream pattern i.e. some amplification with the polar vortex moving to a position east of Greenland which will enable the troublesome trough to eventually move eastwards across the country but not before it has delivered copious amounts of rain.. oh dear the run up to christmas looks a thoroughly miserable wet affair and will do no favour to anyone trying to get in the christmas spirit.

However, more importantly the models are now backing down on the strength of heights to our south, only on the 23rd do we see a pulse of warmer uppers behind the warm front, but these will be kicked aside during Christmas eve and by Christmas Day much of the north at least looks to be in polar maritime air..

Its a very average set up for the time of year.. however, its been a long time since we have experienced a wet and wild run up christmas and perhaps therefore the outlook to many appears thoroughly miserable.

Longer term - signs of strong heights building over Greenland but also those heights lurking to our south with us once again in no-mans land where no doubt another battle between cold and mild will rage..but I don't foresee as much rain next week as we will see in the coming days..

The last week of December is often a pivotal point in the winter season when the northern hemisphere goes through abrupt changes as it settles into its Jan-Feb mid winter state. The transferal of the polar vortex to a position much more favourable for sustained cold is about to take place, but before we get there it looks like we will have to endure a very unsettled average spell of weather where the cold and mild airmasses fight over us.. It could be a whole lot worse for cold snow lovers.. i.e. polar vortex setting up shop over Greenland.

[NorthernRab]

Worrying indeed - what became of the drought warnings of early 2012 for the South? - anyone forecast this? - no - I thought not.......

Did anyone forecast rainfall totals over 5000 hours away? Erm....nope.

That 27th is looking of particular interest if we can get a better tract to the low as it swings round from the North.

[PubliusEnigma]

Yes, ironic how after all the chopping and changing and inconsistency in the NWP, we can now have reasonable confidence in where we are likely to be by days 8-10. And it's not a good place if your looking for cold.

The one thing Ian, that remains consistent throughout the entire ECM run this evening, is the displaced Bartlett which has a more SWesterly positioning close to Iberia, rather than the western Alps. This is a notoriously stubborn feature which can remain in situ for up to four weeks, during the winter months, possibly even longer beyond that. For cold lovers that is the biggest obstacle IMO to any progress towards a wintery set up. It feeds lows in towards the British Isles, endlessly. Its there on all the models for the duration of the run.. Its even there on the GFS way out in FI at T384 bar a 24 hour shuffle around Christmas day. This really does not bode well for anything other than winds generally from a SW or W direction. And in addition quite possibly very high rainfall totals over Christmas, and into January. Almost the opposite of the NW winter forecast in many respects.

[phil nw.]

Just looking through todays CPC discussions and the forecasters state only 2/5 low confidence in the forthcoming pattern over the next 2 weeks.

Full text here http://www.cpc.ncep....day/fxus06.html

Some snippets of interest.

THE OBSERVED POSITIVE HEIGHT ANOMALIES SOUTH OF THE ALEUTIANS ARE FORECAST TO DECREASE CONSIDERABLY,

WHILE LARGER POSITIVE HEIGHT ANOMALIES ARE MORE LIKELY TO DOMINATE OVER

NORTHERN NORTH AMERICA.

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: BELOW AVERAGE, 2 OUT OF 5, DUE TO

GOOD AGREEMENT AMONG ENSEMBLE MEANS, OFFSET BY HIGH UNCERTAINTY IN THE STORM

TRACK SOUTH OF POSITIVE HEIGHT ANOMALIES IN NORTHEASTERN CANADA.

THE ENSEMBLES HAVE COME INTO GOOD AGREEMENT ON HEIGHT RISES ACROSS NEARLY THE ENTIRE NORTHERN TIER OF NORTH AMERICA, INCLUDING EASTERN ALASKA AND WESTERN CANADA. WARMER THAN NORMAL TEMPERATURES ARE FAVORED OVER THE WESTERN PART OF ALASKA IN RESPONSE TO THIS. RISING HEIGHTS OVER ALASKA POINT TOWARD A BETTER CHANCE OF CONTINENTAL AIR IMPACTING THE CONUS, FIRST IN THE NORTHERN ROCKIES.

TELECONNECTIONS BASED ON THE POSITIVE HEIGHT CENTER JUST NORTH OF HUDSON BAY ARE NOT IN GOOD AGREEMENT WITH THE HEIGHT FORECAST FROM ANALOGS. SINCE THE PATTERN CORRELATION BETWEEN THE ANALOG BLEND AND THE MANUAL BLEND IS VERY HIGH,

THIS SUGGESTS THAT THE WEEK-2 PATTERN MIGHT BE TRANSIENT, WITH A POTENTIAL

REALIGNMENT TOWARD A MORE CANONICALLY NEGATIVE AO PATTERN THEREAFTER. WITH A PERSISTENTLY NEGATIVE AO, THE OBSERVED SURFACE HYDROCLIMATE THIS MONTH REMAINS UNUSUAL, PERHAPS UNPRECEDENTED. FURTHER COMPLICATING THE EXTENDED RANGE

FORECAST IS THE LACK OF ROBUST TROPICAL CONVECTION ASSOCIATED WITH THE MJO,

WHICH HAS BEEN LARGELY INACTIVE FOR THE PAST MONTH, AND IS ONLY NOW SHOWING

POTENTIAL SIGNS OF WEAK REORGANIZATION.

The way i read it is the current modelling full of uncertainty.

The upstream jet pattern over NA not yet agreed amongst the Op.runs

Some adjustment to the current wavelengths in week 2 with a change to a lower AO index.

Hopefully the build of polar heights will become extensive enough to impact the UK.eventually.

[chionomaniac]

The one thing Ian, that remains consistent throughout the entire ECM run this evening, is the displaced Bartlett which has a more SWesterly positioning close to Iberia, rather than the western Alps.

Please can you point out the 'displaced' Bartlett in these ECM charts from this evening, PE.

Granted, we have raised heights towards the end of the run and temporary ridging between days 3-4 but that is hardly consistency!

[latitude]

GFS 12z ensembles give some hope again after Christmas

Plenty of members trending cold

You were showing the same looking ensembles last week for this week. Saying cold on the way, now we are here theres no cold, now your saying cold after xmas.

Edited December 19, 2012 by latitude

[ricey076]

Well as there is no hope of cold in the near future, I suppose heavy rain and flooding is the next exciting thing we can hope for.

not exciting for the poor people that get flooded ! Edited December 19, 2012 by ricey076

[shotski]

You were showing the same looking ensembles last week for this week. Saying cold on the way, now we are here theres no cold, now your saying cold after xmas.

That's not what He's saying at all, Ensembles give some hope is what he is saying and he is correct.

Probably half of those members go cold after 25th.

[ICETAB]

It suprises me that nobody has mentioned the JMA at T192.

Anyone got a link to the 12z ECM ensembles. Where did the op sit in relation to other runs?

Edited December 19, 2012 by ICETAB

[Methuselah]

What exactly is a 'displaced' Bartlett?

[AWD]

What exactly is a 'displaced' Bartlett?

A Barlett that's got lost?

[Grimsby Snow Lover]

That's not what He's saying at all, Ensembles give some hope is what he is saying and he is correct.

Probably half of those members go cold after 25th.

Compared with the ensembles from previous days they are a big improvement on the likelyhood of colder temperatures after the 25th. Yesterday they were only a few runs that had -5 850's now we have over half of them at or below -5 850's. A more encouraging step in my book, until the next run anyway.

Edited December 19, 2012 by Grimsby Snow Lover

[DAVID SNOW]

What exactly is a 'displaced' Bartlett?

A Greenland High?

[Summer Sun]

You were showing the same looking ensembles last week for this week. Saying cold on the way, now we are here theres no cold, now your saying cold after xmas.

What I said was the ensembles give some hope I have not said anything is certain, last week I also said there's some hope around Christmas theirs a big difference between "Hope" and "Certain"!

[LomondSnowstorm]

What exactly is a 'displaced' Bartlett?

A high pressure system, sitting anywhere other than right across continental Europe out to the Azores.

Edited December 19, 2012 by LomondSnowstorm