Model Output Discussion 17th Dec.2013-12z onwards.

[Winter Cold]

Hello everyone, im a long time lurker on the model thread, but I wanted to ask a question whilst its a bit quieter....

Ive just read some posts about the 'uppers' and comments along the lines of -3 and -4 arent cold enough for snow.

I keep thinking back to March when we were under -8 uppers and a lot of posters were saying as it was March and the longer days, stronger sun etc that that is exactly what we needed, but many comments were also saying 'if this was December, January we'd be OK with -2 to -4 etc so im just a bit confused.

Were obviously now at the shortest day part of the year so this seems to be the period when ud think these lower uppers would be supportive of snow?

The latest GFS showing -4 to me says snow?

Im probably missing or misunderstanding something but wanted to ask anyway

Thank you to the regular posters who make this forum a great place to learn, i love coming in here and reading and I wish everyone a Happy Christmas

Edited December 25, 2013 by Winter Cold

[Jason M]

Hello everyone, im a long time lurker on the model thread, but I wanted to ask a question whilst its a bit quieter....Ive just read some posts about the 'uppers' and comments along the lines of -3 and -4 arent cold enough for snow.I keep thinking back to March when we were under -8 uppers and a lot of posters were saying as it was March and the longer days, stronger sun etc that that is exactly what we needed, but many comments were also saying 'if this was December, January we'd be OK with -2 to -4 etc so im just a bit confused.Were obviously now at the shortest day part of the year so this seems to be the period when ud think these lower uppers would be supportive of snow?The latest GFS showing -4 to me says snow?Im probably missing or misunderstanding something but wanted to ask anyway Thank you to the regular posters who make this forum a great place to learn, i love coming in here and reading and I wish everyone a Happy Christmas

Wow, where to start :-)

The relationship between 850s and snow is fairly complex tbh.

Others will no doubt disagree but from late Nov to end of Jan a decent rule of thumb is add 7 to the 850 temp to get the ground level temp. So -3 850 gives us +4c at ground level. In most cases this will result in rain / sleet. If snow does fall it won't lay hence my slushfest comment earlier.

Where it gets more complicated is whether the air is Atlantic, arctic, continent sourced. If its Atlantic based the air is more modified at the surface so you could add another couple of degrees. So -3c 850 might give you 6c at ground level. Off a genuine arctic northerly the plus 7 formulae would work okay. From a continental sourced airmass as the air will be colder at lower levels so you could add say 5c. Using the above therefore a full on continental easterly with a -3c 850 might give you plus 2c at ground level. This is adequate for snow in most (not all) cases but obviously it won't lay. This scenario was something we had a lot of last year.

Hope that helps.

Jason

Edit: by mid feb you can another couple of degrees to the 850s in most cases because of increased sun strength.

Edited December 25, 2013 by Jason M

[weatherguy]

Hello everyone, im a long time lurker on the model thread, but I wanted to ask a question whilst its a bit quieter....

Ive just read some posts about the 'uppers' and comments along the lines of -3 and -4 arent cold enough for snow.

I keep thinking back to March when we were under -8 uppers and a lot of posters were saying as it was March and the longer days, stronger sun etc that that is exactly what we needed, but many comments were also saying 'if this was December, January we'd be OK with -2 to -4 etc so im just a bit confused.

Were obviously now at the shortest day part of the year so this seems to be the period when ud think these lower uppers would be supportive of snow?

The latest GFS showing -4 to me says snow?

Im probably missing or misunderstanding something but wanted to ask anyway

Thank you to the regular posters who make this forum a great place to learn, i love coming in here and reading and I wish everyone a Happy Christmas

 

Hi Winter Cold, I'm sure there are other factors relating to the time of year, but in general it's best to think of it like this:

 

If the cold is coming from the north/north west, the air associated with the airmass will be relatively wet.  As a result, colder uppers are required to be sure of snow...Generally you're looking at -5C, perhaps even -6C depending on location/altitude.

 

If the cold is coming from the east/north east/south east, the continental airmass will be dry.  Assuming this airmass is cold, and associated dew points are below 0C, any precipitation is likely to fall as snow as long as the uppers are below 0C also.

 

The GFS' current cold spell in FI is bringing with it a strong maritime influence, meaning -4C uppers would be very marginal in such a set up; some would see snow, particularly in the north and on hills, while those further south may be struggling.  Last March we had a battleground scenario where the atlantic airmass came into contact with the already established easterly feed.  As the LP was to the south of us, more continental air was dragged in, resulting in snow despite the cold established uppers being "mixed" out to around 0C/-1C by the relatively warm atlantic air.

 

Hope this helps answer your question

Edited December 25, 2013 by weatherguy

[ukpaul]

The only snowfall we had here in Guildford last winter was with uppers of around -3 or 4, the benefit being that it was air returning from the continent. It did settle too.

[Winter Cold]

Thankyou Jason and weatherguy for your replies

Ive learnt a whole lot more just there, great stuff!

[SMU]

http://www.meteociel.fr/modeles/ecmwf/runs/2013122512/ECH1-144.GIF?25-0

Big back door heights - more so than the GFS

 

 

S

[Cheshire Freeze]

144 ECM

 

Very interesting

 

[tight isobar]

Personally like outputs take on a likely flip to something intresting.merry Christmas..RIP MUM.:-(

[Cheshire Freeze]

1030 mb high forming over N Scandi there. Can only envisage Se'ly movement of LP being reinforced from there

 

[ARNOTT ad]

After early promise, were then back to square 1

[bluearmy]

not often you see ecm op so different days 7/8.   tells its own story. keep with the ens mean for the time being,

[NorthYorksWeather]

The ECM Northern Hemisphere profile looks very different on the 12z compared to the 00z, heights reaching towards the arctic over Scandi on the 12z rather than the Atlantic. PV looks to regather though tho this time. Certainly a better day model watching from a coldies perspective and looking forward to the 18z.

[Tim Bland]

Day 10 on the ECM looks good with an Atlantic ridge ! http://www.meteociel.fr/modeles/ecmwf.php?ech=72&mode=0&map=0&type=0&archive=0

Edited December 25, 2013 by Tim Bland

[LomondSnowstorm]

The only thing I'd add to the reply about uppers needed for snow is that the highest uppers you could 'get away with' are during rare occasions when there's a cold trough (or a slack flow with very cold surface air) sitting directly over the UK as occured at points in both December 2009 and December 2010. In the former we had falling and lying snow with temperatures of 0C with uppers just below 0C because the air embedded at the surface was so cold and still that relatively less cold air higher up in the atmosphere was unable to mix the cold surface air out. Upper air temperatures above 0C in these instances are what give freezing rain events.

Anyway, the +240 ECM is a decent chart, although with a very slightly positively tilted trough it would be a case of 'will it won't it ridge northwards' before the next low pushes in.

The PV lobe to our northeast is critical too in dragging in that all important cold pool to the Eurasian continent and, eventually (if we're lucky), towards us. Early days but the models are looking a lot more promising for proper HLB than they have done since the start of the month.

[mountain shadow]

After early promise, were then back to square 1

If you reckon this is square one..http://cdn.nwstatic.co.uk/ecmimages/20131225/12/npsh500.240.pngthen is suggest you learn how to read weather charts.

[winterof79]

GFS 12z gets to the ECM 10 day solution eventually

http://modeles.meteociel.fr/modeles/gfs/runs/2013122512/gfsnh-0-348.png?12

Quite similar actually

http://www.meteociel.fr/modeles/ecmwf/runs/2013122512/ECH1-240.GIF?25-0 some sort of mid atlantic ridge in the offing using Greenland to link with the Arctic high

[Grimsby Snow Lover]

If you reckon this is square one..http://cdn.nwstatic.co.uk/ecmimages/20131225/12/npsh500.240.pngthen is suggest you learn how to read weather charts.

Thats probably the best ECM chart of the winter so far

[Gibby]

Good evening folks. Here is this evening's look at the midday outputs of the NWP output for Christmas Day December 25th 2013.

 

All models continue to model very changeable conditions from now all the way up to the New Year with spells of rain and very windy weather with severe gales on Friday. There will be plenty of rain on Friday and again later on Sunday and also at various other stops on the way up to the New Year. At other times there will be sunshine and showers, wintry on hills in the North. Temperatures will remain close to average and rather colder in the North at times and rather mild at times in the South especially early next week.

 

GFS shows the New Year period windy and wet with Low pressure crossing the UK on New Years Day with a showery NW flow following with snow showers on Northern hills. Through the first week of the year the weather remains very changeable and often wet with sunshine and wintry showers alternating with heavier and more persistent rain. Temperatures will gradually turn rather colder with time extending the wintry risk to lower levels later.

 

UKMO closes tonight's run with a mild and windy SW flow carrying rain at times across the UK in the continuing unsettled mood.

 

GEM continues wet and unsettled all the way up to Day 10 which of course includes the New Year.There will be ample spells of rain and showers for all with Low pressure always close to Northern Britain in a broad Westerly flow.

 

NAVGEM too shows unsettled weather persisting over the UK with rain or showers at times, the showers heavy and wintry on northern hills at times.

 

ECM tonight also shows unsettled weather continuing up to the New Year with rain and showers at times with brief drier spells in between and temperatures close to average. later there are signs of a change to rather colder NW winds and wintry showers in 10 days time.

 

The GFS Ensembles show the changeable and average temperature type weather conditions going throughout the run with little sign of any pattern change away from the general idea  and bias towards low pressure remaining close to the North of the UK with wind and rain at times.

 

The Jet Stream forecast remains unchanged from this morning with an incessant flow from the West over or just to the South of the UK.

 

In Summary the weather will continue changeable and unsettled over the next couple of weeks. Events for the period up to the New Year are quite agreed upon between the models but changes thereafter are more varied but quite modest with little concrete evidence of any shift towards anything colder and more traditionally wintry in the near future.

Edited December 25, 2013 by Gibby

[cold snap]

Good evening,

Need to get the cold artic air away from Eastern America with that energy coming west it's hard to get any building of heights however both GFS and ECM have a little go at a split

Mild air in Central Europe not helping heights either ,

Edited December 25, 2013 by cold snap

[Methuselah]

 

In Summary the weather will continue changeable and unsettled over the next couple of weeks. Events for the period up to the New Year are quite agreed upon between the models but changes thereafter are more varied but quite modest with little concrete evidence of any shift towards anything colder and more traditionally wintry in the near future.

Well put, Gibby...We are still a long way from seeing anything properly wintry, IMO: a few days' maxes between 3-6C and some sleety showers isn't all that much to get excited about...It'll come, though, just not quite yet!

[SMU]

http://www.meteociel.fr/modeles/ecmwf/runs/2013122512/EDH101-168.GIF?25-0

 

Day 7 Ensemble MEAN strong correlation with the ECM operational -

 

Also a good strong declining curve to day 15.

 

Expect a colder ECM DET 32 on the next update.

 

A while to wait- but our best chance of cold so far this winter......

 

S

[ARNOTT ad]

Steve I love your posts!!

[Joe Levy]

To my eyes, the 18z GFS is better at 144 hours, but someone correct me if they think otherwise! Ridging between Scandinavia and the Arctic and a better tilt on the Atlantic low.

Edited December 25, 2013 by Joe Levy

[Jason M]

yep, better.

 

Better heights to the NE and on this run some colder uppers get pushed into northern Scandi which could be useful further down the line

 

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=150&mode=1

Edited December 25, 2013 by Jason M

[Cheshire Freeze]

yep, better.

 

Better heights to the NE and on this run some colder uppers get pushed into northern Scandi which could be useful further down the line

 

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=150&mode=1

 

The low can't push any further than the UK due to pressure rises to the E/NE. There is also an attempt at trough disruption & energy trying to head SE. Looks better than the 12z thus far and could be a good FI (usual disclaimers apply).