Model Output Discussion - 23rd Jan - 12z onwards

[Ali1977]

Weather onlines week ahead forecast goes against most of the weather models I've seen and doesn't bring in the cold to next Sunday, anyone know which long range they use?

[Daniel*]

@EssexWeather: @bwdloyal Ensembles take a hit around the 1st of Feb. MOGREPS has strong agreement for a potent Northerly mid-run. All to play for :-)

Which toys with the recent medium range update, MO - so there is room to be optimistic. Albeit it is tempered by past disappointment but if I'm right the last 'cold spell' was never really on MO agenda. While we were drooling, perhaps cherry picking at times at the core it was translucent. This might be different.

6z would get the masses in - promising signs that we might get +ve linking up to Greenland.

Notice the spike in PPN with relatively cold uppers you get the jist. Best chance for S to join in IMHO.

Edited January 24, 2015 by Daniel*

[IDO]

@EssexWeather: @bwdloyal Ensembles take a hit around the 1st of Feb. MOGREPS has strong agreement for a potent Northerly mid-run. All to play for :-)

Which toys with the recent medium range update, MO - so there is room to be optimistic. Albeit it is tempered by past disappointment but if I'm right the last 'cold spell' was never really on MO agenda. While we were drooling, perhaps cherry picking at times at the core it was translucent. This might be different.

6z would get the masses in - promising signs that we might get +ve linking up to Greenland.

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Notice the spike in PPN with relatively cold uppers you get the jist. Best chance for S to join in IMHO.

 

You notice the spike in precipitation coincides with the uppers rising from -5 to -2 on the op. The dreaded warming from a deep low. We need about -6 uppers for a 50% chance of snow at sea level so the op looks mainly rain, with possibly back edge snow. However the op is an outlier for precipitation amount for that time so is unlikely to be representative of the final outcome. As usual with the south lots of variables need to be right for snow.

[geordiekev]

It has to be said, was GFS even interested in such an outcome just a couple of days ago? I looked at the Manchester 850hpa ensembles for Thursday GFS 0z and it wasn't.

If it comes off, it seems to have snuck up on GFS this one.

I, like so many others are still testing the ice sought of speak as I recall the last 2 cold spells also popped up on the charts just before the weekend and then on the Sunday vanished.

The threads went into meltdown and was not a pretty place to visit if I'm honest, but strangely both spells popped up again on the Monday/Tuesday and verified of sorts.

I am just mentioning this as a reminder as Sunday looms. Please be kind, the trends are there and this time it's more within the reliable timeframe. In any case it looks wintry, I don't expect every square inch of the UK to have lying snow but with Azores displaced and the vortex emptying into Europe these are amazing synoptics and have screamed reload since the Azores high went on an Atlantic cruise at Xmas time, so enjoy the ride we've waited long enough.

[winterof79]

You notice the spike in precipitation coincides with the uppers rising from -5 to -2 on the op. The dreaded warming from a deep low. We need about -6 uppers for a 50% chance of snow at sea level so the op looks mainly rain, with possibly back edge snow. However the op is an outlier for precipitation amount for that time so is unlikely to be representative of the final outcome. As usual with the south lots of variables need to be right for snow.

 

 

I feel there will be ample opportunity for snowfall after Tuesday.

 

 

 

My cups over half full and i am due a top up at 16z......

Edited January 24, 2015 by winterof79

[492]

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

 

8-10 day 500mb anomaly charts show a deep trough over mid USA and another over western Europe giving a particularly long wavelength. If the wavelength is sufficiently long the waves can become stationary or even start to move backwards i.e. retrogression..

[Mark Bayley]

I suspect the GFS is overdoing precipitation on Wednesday, or at least the snow potential. A glance at the NetWx-MR suggests some back edge snow as the front clears south, with accumulations to high ground perhaps? Nothing extraordinary. Behind it snow showers will pile into NI, Western Scotland, NW England and Wales (with overnight accumulations). Perhaps some making it far inland given the strength of the wind (e.g. Cheshire gap). Looking less good with distance south and east (e.g. worst locations probably SE Midlands, SW, Southern England, SE and EA). Friday sees the potential for weak front to progress southwards overnight, although associated with a milder sector (so marginal snow situation to low ground) and further south. All subject to change of course. Thereafter the potential for a sliders and winds to swing north easterly. Plenty of snow opportunities in the coming week, although i understand why those in aforementioned region may feel disappointed, given these regions are more likely to 'miss out', or at least within the next several days

 

Wednesday day

Wednesday night/Thursday day

Friday night

   

Edited January 24, 2015 by Mark Bayley

[bluearmy]

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

 

8-10 day 500mb anomaly charts show a deep trough over mid USA and another over western Europe giving a particularly long wavelength. If the wavelength is sufficiently long the waves can become stationary or even start to move backwards i.e. retrogression..

Or they can flatten out and even lengthen further. Now you've mentioned retrogression, watch the wavelength shorten so much that we end up the wrong side of a -NAO with a balmy souester! nothing would surprise me given our recent record on cold spells.

[legritter]

Very good potential on todays charts so far .And if the pattern what is currently modelled for next weekend comes off i,m hoping for some features to turn up to give snow for many .But at this range we can only follow all models for the general flow .so plenty of caution from us snow lovers needed but i realy do hope many of us can see some snow and smell that Arctic air .Fax charts very usefull in this set up so i,m looking forward to some very interesting model chat from us Hunters of cold weather synoptics ,bring it on ,cheers all   

[Mucka]

Once bitten, twice shy.

Except coldies have been bitten often and generally aren't shy about promoting snow chances. 

Still, there is a lot of caution about over-hyping the upcoming cold prospects after a long largely snowless winter for many and yet had we seen this charts in early Dec the forum would have gone into meltdown. Such are the manic moods of the Coldie.

 

I was pretty dismissive the other day of this being anymore than a 3 day toppler but rather than back off the models have continued to reinforce cold prospects.

It looks quite exciting for the North thus far with wintry showers likely pushing in as early as Wednesday evening.

The main reservation is about how much modification of the polar air there will be given the track and and close proximity of the trough to the UK but the initial Northwesterly looks very cold across all output and it is only as winds swing more into the N/NE where any warm sectors will ironically be as they circulate around the associated low before we can more directly draw in the colder air again. 

 

As things stand I think the NW is best placed all around, at least the first few days and anywhere in these regions with a little elevation could see a lot of snow.

Very hard to say if it will be cold enough for any snow to low levels to accumulate.

 

I think this initial phase of any cold snap/spell is pretty much locked in given it is a fairly basic setup, only detail will change with the shape and depth of the trough.

 

Still likely cold into the weekend but from here uncertainty increases. Will the Atlantic ridge hold and renew? If it does will it ridge into Greenland or topple and flatten or cause low pressure to disrupt behind and push WAA toward Scandinavia? Will we see something less clear-cut and messy?

 

Certainly the output has been moving toward stronger blocking, at least MLB, as we move into Feb and with a  weak vortex under attack and high pressure beginning to make its presence felt over the Arctic we could be in business. 

 

Did anyone hear that growling? 

Edited January 24, 2015 by Mucka

[bluearmy]

Mucka - the warmer uppers are driven to our ne over the next few days by the sw flow. Any change in that and the lows will spawn in a colder airmass.

[IDO]

Mucka - the warmer uppers are driven to our ne over the next few days by the sw flow. Any change in that and the lows will spawn in a colder airmass.

 

I think Mucka meant the milder uppers as later next week the low to our NE warms out the uppers: 

 

Edited January 24, 2015 by i'm dreaming of...

[Mucka]

Mucka - the warmer uppers are driven to our ne over the next few days by the sw flow. Any change in that and the lows will spawn in a colder airmass.

 

Yes indeed but the models are good with zonal and if the AH is displaced with associated Atlantic ridge the jet upstream will be aligned to our North so hard to see how we can avoid some warmer air being pushed toward Scandi (Edit, Should read ahead and behind) behind our trough and entering the circulation IMO especially as this all occurs in fairly immediate time-frames.

How much warm air, how warm, how it mixes and how quickly it is pushed back South after the initial Northwesterly is all up for grabs though. 

Edited January 24, 2015 by Mucka

[Frosty.]

Well I'm now expecting 7-10 days of cold unsettled weather starting next Wednesday with an increasing risk of snow, ice and frosts, and no mild sectors, none of this constant chopping and changing from day to day. IMO this will be the best cold spell of the winter so far although for those in southern England who have had next to nothing wintry so far. The only way is up..and there is now cross the board emphatic support for a cold outbreak which is set to last at least a week..not just me saying that either, the MO update today is the most wintry 6-15 day so far...by a country mile.

Edited January 24, 2015 by Frosty.

[Nick F]

I suspect the GFS is overdoing precipitation on Wednesday, or at least the snow potential. A glance at the NetWx-MR suggests some back edge snow as the front clears south, with accumulations to high ground perhaps? Nothing extraordinary.

 

I think 06z GFS is too bullish with the nationwide back edge snow signal on Wednesday. GFS showed, in advance, back edge snow for the cold front that passed through last night. But normally the switch to a cold northwest flow behind a cold front, the air cold/dry enough to support snow lags too far behind for a back edge snow events - normally these back edge events are reserved for direct arctic northerly flows.

 

Nevertheless, northwesterly airmass should turn cold enough following the cold front for snow showers across northern and western areas on Wednesday.

 

I can see where there is some negativity creeping in thereafter to the end of the week though, as the main parent low is rather slow-moving - centred  just NE of the UK for the rest of the week, so the cold feed tends to get mixed out by relatively milder being drawn in on its eastern flank while it sits there.

 

This problem maybe overcome if we can get the low to shift east a little to give a direct northerly feed by the weekend with a re-supply of deeper cold air. GFS, ECM and UKMO all do this, but unfoirtunately 06z GFS doesn't build the ridge to the west solidly and far enough north next weekend to stop 'spolier' lows from moving E or SE south of Greenland and merging with the parent low just to our east and cutting off the cold northerly flow.

 

So some uncertainties once the intial NWly cold blast moves in Weds then mixes out a little through Thursday, i.e. will we get a potent northerly by the weekend that last a few days or more or will it be brief 1 day toppler? Hard call until the models firm up more on how much amplification we get upstream by the weekend.

Edited January 24, 2015 by Nick F

[The Beast From The East]

Hi, could someone just tell me why it is that the BBC weather forcast for this weekend and on into next week with even a mention of the first week in feb shows cold, mild, then cold but only talk of rain and no mention of the S word?

http://www.bbc.co.uk/weather/feeds/30958304

Trying to read the models myself and reading the post on here but it looks like there is potential for a cold snap/spell with some places seeing snow as we go into the middle to late part of next week.

Is it that the BBC forcast could already be outdated or is it a case that they are getting a lot better information from sources we don't have acces to?

Just curious that's all..

Many thank in advance.

[Mark Bayley]

@ Nick: Agreed, back edge snow rather limited (perhaps high ground in the north, i.e. pennies). A better opportunity comes from the snow showers on Wednesday, which i suspect could make decent distance in land. Although like you understand peoples frustrations, especially those towards the south east. Long range ECM looking interesting with a mid-Atlantic ridge and the PV shunted west of Greenland. Whether the ECM is over amplified and overdone the PV split remains to be seen!  

Edited January 24, 2015 by Mark Bayley

[MR EXTREMES]

i know its early in the gfs run but already looks like a pressure build right through the center of the pole.

i expect to see proper heights build spliting the vortex.

im ready to ramp tonight ive a very good feeling this time its heading towards a more meaningful cold spell.

of coarse might be jumping the gun but we shall see.

 

and a futher push on the trop vortex.

polar air already knocking on our door like this morning and last nights runs.

Edited January 24, 2015 by emotional rollercoaster

[shaky]

That is one screamer of a northwesterly on the 12z run at 96 hours!! All the way from the greenland/canadian area!!

[mcweather]

Before the 12z's roll out lets look at what we have, well we have a progged northerly next weekend first picked up by GFS then joined by ECM  and then very shortly after that by the METO.

 

We are told that we cannot believe anything unless we have cross model agreement. Yet the  cross model agreement on a change to cold at that range is pretty impressive. Reminiscent to a certain extent of the cross model agreement in Nov 2010 albeit for a different cold scenario.

 

Much to be excited about really ( despite the musings of some battle weary model watchers) Such an unstable northerly would almost certainly have  troughs/ disturbances/ possibly polar lows embedded.

 

Bearing in mind the expected upstream pattern from NCEP etc, if anything I would expect the charts to upgrade as we approach the anticipated event rather than the opposite.

[Cloud 10]

UKMO and GFS at 120 hrs,UKMO makes much less of the Canadian vortex and is much better downstream.

 

ukmo..  gfs..

[Mucka]

Another stonking UKMO

 

[mcweather]

Some interesting little features crossing the south west of England in -5 850's and sub 528 thicknesses next weekend on this GFS run.

Edited January 24, 2015 by mcweather

[Paul_1978]

And the low pressure sinking ever south at T +186 whilst the Atlantic is looking reasonably blocked with nothing able to come across the top?

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=186&mode=0

[mulzy]

Another stonking UKMO

 

 

Can anyone work out the thicknesses over the UK.  I'm guessing 525-530?

 

Great to look at but I fear not much precipitation and any that falls will be slushy sleet away from prone spots!

Edited January 24, 2015 by mulzy