Model Output Discussion - 16th Jan 12z onwards - Smile While You Post!

[Frosty.]

The week ahead looks cold, the first nationwide cold spell of this winter actually. The GEFS 06z mean gives an idea of how close we are to an impressive sequence of borderline ice days but the most interesting feature of the week ahead is the precipitation, there will be snow in places, perhaps significant falls whilst other areas have rain and sleet but also decent gaps of fine weather with sharp frosts and freezing fog, it's a very complex picture as fronts try to push east and then stall, pivot and perhaps even being forced to retreat west again. Areas which miss the frontal ppn will be mainly coastal areas of the north and east but they will have wintry showers with a risk of snow, into next weekend, the colder air may finally be shunted east with conditions moderating but the further outlook indicates temperatures will oscillate markedly from day to day with an ongoing risk of snow and frosts at times between short lived, milder, wet spells...The bottom line is, it's a wintry week ahead with lots of lamp post and radar fun. :-)

[Nick F]

While we enjoy a lull between the model runs, some of my thoughts on how this cold spell may pan out:

 

Saturday

A cold W to NWly flow covers the UK today, an occluded frontal system embedded in this flow brought enhanced bands of wintry showers across many areas this morning. One band of showers, now clearing the far SE of England brought a mixture of sleet, snow and freezing rain. The rain bought some hazardous driving conditions across SW and central S England this morning, falling on frozen surfaces. Drier and sunnier conditions for many this afternoon, though rain showers continuing across SW England and Wales, falling as snow over the top of the Moors and Welsh Hills. Further sleet and snow showers continue across northern and western areas though, particularly across western Scotland, NW EIRE, N. Ireland and NW England, where they will continue to fall as snow even to lower levels away from coasts, topping up the snow already on the ground across these areas.

 

Tonight

Clear spells across northern areas tonight leading to a widespread frost, with temperatures well below freezing over the snowfields, however, as winds turn northerly we will see a few troughs or fronts moving south, bringing bands of snow showers south at times. Cloudier across southern areas overnight, keeping temperatures generally a few degrees above freezing. Also, we will see outbreaks of rain/sleet spread in overnight from the west across S Wales and southern counties of England (as far N as Midlands and Sern E Anglia) – turning to snow on its northern edge – particularly, but not exclusively over higher ground, so we could see a light covering in places by dawn.

 

Sunday

Overnight rain, sleet and snow clearing the far south by mid-Sunday morning, then a cold northerly flow spreads south across all areas, bringing sunny spells but also some wintry showers – these becoming confined to northern and eastern Scotland and NE England by the afternoon. Generally cold, more particularly in the north. Sunday night is looking particularly cold though across many areas under clearing skies. Towns and cities in the north down to-3 to -4C, in the south 0 to -2C. But in rural areas we could be looking at as low as -10 to -14C across the snow fields in sheltered parts of Scotland, N England and N Ireland ... -4 to -7C across inland rural parts of Wales, central and S England.

 

Monday

Monday’s looking generally dry, bright or sunny across the UK, though a shallow area of low pressure across the North Sea looks to create enough instability and frontal activity for some wintry showers towards eastern coasts.

 

Tuesday

Then Monday night/Tuesday morning, we see an Atlantic frontal system push in from the west , and as this bumps into the cold air in place, rain/sleet looks to turn to snow across Scotland, N England and Wales. A bit less clear cut further south, perhaps falling as rain/sleet initially across S England and E Anglia but *maybe* turning to snow as it clears. Given the uncertainty over how far east the front progresses and also the potential for a low to develop along it across southern England (as per UKMO fax and 00z ECM deterministic), all of which may not be modelled too well this far off, given cold air in place and model difficulties at handling trough-disruption, confidence is low by Tuesday where rain/sleet and snow will be.

 

Wednesday

On Wednesday GFS and ECMWF show another Atlantic frontal system push south and east off the Atlantic ahead of a low pressure system dropping SE from Iceland area. With cold air in place but less cold air perhaps getting entrained into the circulation of the low dropping south, again some uncertainties of where will see rain/sleet/snow. To complicate matters, 06z GFS and 00z ECM differ on depth and track of the low moving SE. Shallower 00z ECMWF solution would bring less mixing and perhaps more of a snow than rain signal. A deep low as per GFS, would drag less cold air into thecirculation.

 

Late week and beyond

Beyond Wednesday, the models diverge too much to have confidence, perhaps a brief easterly to end the week between weak ridge building north of the UK and low pressure over mainland Europe. Operational guidance of  NWP models so far today and last few days attempt to return the UK to a more mobile (and milder) westerly regime by the end of the week or next weekend. But there is enough spread in the GEFS ensembles and lack of confidence in resolving even mid-week trough disruption to suggest a return to milder conditions is a dead cert. A look at some 06z GEFS shows the Azores high still ridge NE near Nern UK next weekend – which would keep the more mobile Atlantic return at bay.

 

06z GEFS for 12z Saturday 24th Jan

Edited January 17, 2015 by Nick F

[nick sussex]

I think the issue going forward isn't so much that there might be increased Atlantic mobility but what happens to this as it hits western Europe.

 

Even before this the earlier timeframe will either give a stronger foundation to resist this or one in which higher pressure will be swiftly pushed eastwards.

 

The earlier possible slider lows play a role in where any high might be, the ECM postage stamps show varied solutions, some of which are past the point of no return as in too much energy is already going over the top.

 

You'll essentially be able to build the future picture by what happens at least initially before T120hrs, your base point will be the first proper slider between T96 and T120hrs, if this corrects westward then high pressure to the east/ne will also edge west this will likely then translate to the next slider also sliding further west, this delivery of energy into our " bellwether" troughing over northern Italy will help to inflate any high to the east/ne.

 

The reason for highlighting that troughing over northern Italy is that this strongly correlates with a displaced Azores high and higher pressure north of it, its like two boxers trying to floor one another, the Atlantic desperately trying to push the Azores high east, the northern Italy low blocking its progress.

 

The tipping point will be reached when one basically waves the white flag, so if the Atlantic loses energy will disrupt se and head towards northern Italy, the remaining energy goes north.

 

At this point we don't know for sure what will happen but for cold hopes you can lower the odds in tandem with corrections westward and vice versa.

 

However to have a fighting chance we need to see solid early foundations.

[SMU]

A quick comment before the 12s roll- my only comment infact!!

 

The 12z GFS has a feature at around 120 -126 that provides the WAA & breakdown to the cold over the UK,

Its the low moving ENE over Eastern greenland -

 

From this output I expect the GFS to start making corrections to it digging south in the form of a secondary slider - bringing more snow across particularly the East of the UK

 

http://modeles.meteociel.fr/modeles/gfs/runs/2015011706/gfs-0-126.png?6

 

One to watch

S

[Snowy L]

Looks like we have snow in the Northeast to watch out for during Monday before the main weather front pushes in from the west

 

Edit; Much smaller warm sector on this run, could see an all snow event for many Northern areas.

Edited January 17, 2015 by Snowy L

[shaky]

No changes for the better or worse on this run!! Same as 00z and 06z!

[Snowy L]

Looking good with high pressure further West on this run, need that next low in the North Atlantic to undercut though. On current charts it's oriented SW to NE, we want SE to NW or at least S to N.

 

http://www.wetterzentrale.de/pics/Rtavn1141.gif

[Winter Cold]

A nice enough T120 from GFS 12z tonight. Its still maintaining the slider low and this looks to be getting an easterly going:

 

[Captain Shortwave]

GFS day 4

 

UKMO

 

The GFS manages to separate the Iceland flow and send it south east as a cut off low into Europe, which sets up an easterly later on with showers pushing in off the north sea. The UKMO still has an elongated trough through the UK up to Iceland.

Edited January 17, 2015 by Captain shortwave

[Blake]

GFS 6h and 12h for Thurs 7am

 

 

Slightly strong heights over Greenland with westward correction of low to the south.

 

Scandi heights marginally stronger and slightly further NW. Low over southern UK slightly further north...

 

Wonder if the Scandi heights can find a way to link up with Greenland heights down the line with weaker LP putting up less of a fight against the heights to our N/E? If so we could end up with a slider?

Edited January 17, 2015 by GUWeather

[Jason M]

I think we are really going to struggle for a major snow event this week as the temperature profile just doesn't look supportive. I think in the north with some modest elevation it's a maybe, but down south on lowish ground I just don't see it.

The 528 dam line is supportive for much of the week, but we come back to the fact it's a maritime based flow and 528 dam won't neccersarily cut it.

For instance take the chart below, we really need values of 10 or less and through this week were just not seeing it.

http://www.meteociel.fr/modeles/gfse_cartes.php?ech=90&code=0&mode=6

If later on we get a continental undercut this will change the position dramatically, but 850s and temp profile just look slightly the wrong side of marginal. This is really because the initial northerly has not got the potentency needed to get some Arctic air into the mix.

In old money it looks like being a 'rather cold' week rather than a truly cold week. Don't get me wrong I'm not saying some won't see snow, indeed most may see some wintryness, but a big snow event..... Not so sure.....

Edit by 120 with an easterly flow much better. Shows how important continental sourced air is

Edited January 17, 2015 by Jason M

[shaky]

Compare the 120 hour chart from ukmo yesterday to the 96 hour chart today and todays is better! ! Slacker more of a sausage low and scandi high further west!!

[Ice Day]

Another small improvement on the GFS 12z vs the 6z.  Nice uppers at 138 as well, baby steps and all that but any improvement is gratefully received!

 

 

[Barry12]

The cold spell looks to last into Friday now with -6 uppers still around

 

 

Considering the GFS showed a break down on Wednesday on yesterdays 12z, this is a good improvement, lets hope this continues

Edited January 17, 2015 by Barry95

[i luv snow]

I think we are really going to struggle for a major snow event this week as the temperature profile just doesn't look supportive. I think in the north with some modest elevation it's a maybe, but down south on lowish ground I just don't see it.

 

 

I disagree, the north with some modest elevation, maybe? The charts show ppn turning readily to snow across midlands and north. Already this weekend, places in Scotland, NI, WALES!!! and Northern England have seen lots of snowfall, and I don't see how this will be rain anywhere away from southern coastal counties early next week.

 

Ongoing snow prospects are still up in the air as models play with various outcomes but I think the cold air will definitely be snow for a good chunk of the country Monday to Wednesday, especially those places already enjoying snow.

Edited January 17, 2015 by i luv snow

[Cloud 10]

No confidence in anything past 72 hrs at the moment,and certainly not at day 5 which is FI 

 

gfs,,  ukmo..

 

 

Smile while you post.

[Snow Grain]

I love these everything's further west comments we see with every run.

So far on this run there is no real change at the moment. Our snow fortunes will only improve if we start picking up a continental feed. Time will tell.

[Barry12]

Is it any wonder people get confused !!!

 

Shaky was talking about 96 hours, NBLSB was talking about 120 hours...

 

 

I love these everything's further west comments we see with every run.

So far on this run there is no real change at the moment. Our snow fortunes will only improve if we start picking up a continental feed. Time will tell.

 

The cold spell lasts an extra 48 hours, and it's not just the airflow that increases chances of snow. Some continental feeds can be dry.

Edited January 17, 2015 by Barry95

[No Balls Like Snow Balls]

Is it any wonder people get confused !!!

Not really!! i understand what Shaky means. Ie the 120 of yesterday is now todays t96. And well todays t120 is todays t120 LOL

[mountain shadow]

No confidence in anything past 72 hrs at the moment,and certainly not at day 5 which is FI 

 

gfs,,gfs-0-120.png  ukmo..UW120-21.gif

 

 

Smile while you post.

Chalk and cheese, however, even if the UKMO turns out right a Northerly would follow a couple of days later. Whilst there is no deep cold modelled at present, things will stay below average for most.

[SW Saltire]

I'm sure it was noted last winter (or the one before) that the resolution of the UKMO model is very high out to t-72/t-96 but falls of a cliff at 120 and more particularly 144....

*straw clutching*

I'll get my coat...

[SMU]

People saying only snow for the north???

 

Please revisit after you understand what implications the surface cold pool has....

 

 

UKMO is decent for snow for the whole spine of the UK...

 

GFS starting to amplify at 120-150 but not enough this run..

 

S

[john mac]

People saying only snow for the north???

 

Please revisit after you understand what implications the surface cold pool has....

 

 

UKMO is decent for snow for the whole spine of the UK...

 

GFS starting to amplify at 120-150 but not enough this run..

 

S

Cheers Steve, I think people need to look at the bigger picture, as has been said before cold uppers aren't the only thing that will determine whether we get snow or not. Today's runs are definitely more positive than yesterday's!!

[A.J]

some completely off topic rubbish (and that's putting it mildly) removed from the thread........this is not a thread for a country popularity contest, so no more posts on this please and keep on topic please

[i luv snow]

People saying only snow for the north???

 

Please revisit after you understand what implications the surface cold pool has....

 

 

UKMO is decent for snow for the whole spine of the UK...

 

GFS starting to amplify at 120-150 but not enough this run..

 

S

 

Finally, people need to pay attention to this post.

 

Just to clarify my position, I certainly dont think this will only be snow for the north - but the comment re: 'north with elevation, maybe' is misleading as models currently show snow for most of UK Monday to Wednesday via two fronts, maybe marginal for far southern coastal counties but that's not a given either. So people need ot show some patience and let the models firm up on next weeks opportunities! All to play for IMO.