Model output discussion - the beast arrives

[SnowBear]

10 minutes ago, Ruzzi said:

 

Edited February 27, 2018 by SnowBear
Weird double post

[Higher Ground]

9 minutes ago, Quicksilver1989 said:

Finally coming to a consensus on the 00z GFS ensembles it appears, with cold air hanging on for another day. Many ensemble members show maximums around freezing on Saturday now, can we also get Sunday to join in with the cold? I'm not getting my hopes up but fingers crossed....

Thank you so much for coming up with this metric, and updating it consistently over the last few days. It really helps to have an objective way of trying to determine if there really have been 'downgrades' or 'upgrades' over time.

[Derecho]

3 minutes ago, Higher Ground said:

Thank you so much for coming up with this metric, and updating it consistently over the last few days. It really helps to have an objective way of trying to determine if there really have been 'downgrades' or 'upgrades' over time.

Thanks, yup for the Midlands saturday looks like as though temperatures will struggle to get above freezing, support is widespread for a warm up on Sunday though sadly but small changes and that could look a lot better.

Something like P7 with a few southwards adjustments would do me very nicely.

Edited February 27, 2018 by Quicksilver1989

[Hocus Pocus]

The cold continues for many in the North, no deep cold uppers from the weekend but surface cold will keep temps a few degrees above freezing during the day with snow comtnuing to be a risk for the next 5-7 days. Excellent for the time of year.

[Higher Ground]

40 minutes ago, Quicksilver1989 said:

Thanks, yup for the Midlands saturday looks like as though temperatures will struggle to get above freezing, support is widespread for a warm up on Sunday though sadly but small changes and that could look a lot better.

Something like P7 with a few southwards adjustments would do me very nicely.

In terms of wanting to see a historic cold & snowy spell, I actually wouldn't change a single frame of the GFS 0z op run, for my location in the Midlands at least. At any 'normal' time I suspect model-watchers would regard most of the synoptics we're seeing as phenomenal or even borderline impossible - certainly for the time of year. Surely there's a very tricky compromise between hanging onto the coldest air, and allowing enough moisture to feed in to produce snow - even though the moisture is inevitably associated with milder air. I think GFS 6z strikes this balance very well, and still leaves scope for almost everyone to see significant snow depending on subtle changes closer to the time. Tantalising as it is for those in the most southern/south-western areas, it's their knife-edge situation that corresponds to the greatest chances of a nation-wide snow fest. (As I understand things, at least). 

Edited February 27, 2018 by Higher Ground
changed 6z to 0z

[Tog]

Snow in Northern Channel Island 8cm, no snow in the South but very cold, shows how a few miles makes a big difference, I can even see them from my home. Warms up Friday, been consistent with that for days now,  southerly winds Sat, and Sunday forecast 9c. Still have Thursday as the ‘snow event ‘ for all. 

Weather radar, satellite images all on this site, current chart on Aviation tab. Slower than usual to load,  guess the local population is on snow watch and further South grumbling that the others have all the fun! 

https://www.gov.je/Weather/Pages/Radar.aspx

[Summer Sun]

00z Euro 4

[Derecho]

4 minutes ago, Higher Ground said:

In terms of wanting to see a historic cold & snowy spell, I actually wouldn't change a single frame of the GFS 6z op run, for my location in the Midlands at least. At any 'normal' time I suspect model-watchers would regard most of the synoptics we're seeing as phenomenal or even borderline impossible - certainly for the time of year. Surely there's a very tricky compromise between hanging onto the coldest air, and allowing enough moisture to feed in to produce snow - even though the moisture is inevitably associated with milder air. I think GFS 6z strikes this balance very well, and still leaves scope for almost everyone to see significant snow depending on subtle changes closer to the time. Tantalising as it is for those in the most southern/south-western areas, it's their knife-edge situation that corresponds to the greatest chances of a nation-wide snow fest. (As I understand things, at least). 

Yes for the Midlands maxima is still struggling by Monday, although by then dew points have risen to the extent that any precipitation would fall as rain. The best scenario for all would be:

1) The cold air fights off the incoming milder air from the Atlantic
2) Cold uppers move in off the back of an eastward moving low.
3) The angle of attack changes from S-N to SW-NE with pressure increasing over Scandinavia.

A big ask but you never know. The 00z would certainly leave the far north more then happy.

[MR EXTREMES]

27 minutes ago, Quicksilver1989 said:

Thanks, yup for the Midlands saturday looks like as though temperatures will struggle to get above freezing, support is widespread for a warm up on Sunday though sadly but small changes and that could look a lot better.

Something like P7 with a few southwards adjustments would do me very nicely.

Absolutely agree.

so far it's been very underwhelming here on the south coast interesting how quickly this cold spell passes considering the excellent stratosphere event.

Watching the news with Envy hoping we get some channel runners today tonight or tomorrow,

before them milder uppers roll in through Friday.

Someone's said yesterday about the lack of vortex over in the northern side of united states which possibly could have blocked the heights from moving so quickly through Greenland.

Agree also I can't see the cold coming back although few days ago I had high hopes.

But cross model agreement of breakdown into the weekend I wouldn't be surprised to see milder air sweeping even further north on the 12z later.

Very fluent pattern,

fingers crossed for southerners and southwest over the next two days maybe we could squeeze a cm or 2 I'd be happy with that.

 

[Higher Ground]

6 minutes ago, Quicksilver1989 said:

Yes for the Midlands maxima is still struggling by Monday, although by then dew points have risen to the extent that any precipitation would fall as rain. The best scenario for all would be:

1) The cold air fights off the incoming milder air from the Atlantic
2) Cold uppers move in off the back of an eastward moving low.
3) The angle of attack changes from S-N to SW-NE with pressure increasing over Scandinavia.

A big ask but you never know. The 00z would certainly leave the far north more then happy.

Are you sure re the dew points and precipitation?

https://www.meteociel.fr/modeles/gfse_cartes.php?&ech=156&mode=2

Edited February 27, 2018 by Higher Ground
didn't specify monday's chart

[Derecho]

2 minutes ago, Higher Ground said:

Are you sure re the dew points and precipitation?

https://www.meteociel.fr/modeles/gfse_cartes.php?ech=6&code=0&mode=2

It would be extremely marginal for the north Midlands going by my rule of thumb. This is what I normally use as a quick guide:

Add together the Dew point and the temperature  = A
then if:-
If A > 7 prob. snow is very small
If A=7 prob. snow = 10%
A=6  20%
A=5 30%
A=4 40%
A=3 50%
A=2 60%
A=1 70%
A=0 80% or more

Judging by Monday's dewpoints and 2m temps I'd go for a 40-60% in that instance.  For Friday's event A doesn't rise above 0 until midnight saturday down here in Southampton.

Someone with more knowledge may be able to clarify further though.

[FetchCB]

16 minutes ago, Quicksilver1989 said:

It would be extremely marginal for the north Midlands going by my rule of thumb. This is what I normally use as a quick guide:

Add together the Dew point and the temperature  = A
then if:-
If A > 7 prob. snow is very small
If A=7 prob. snow = 10%
A=6  20%
A=5 30%
A=4 40%
A=3 50%
A=2 60%
A=1 70%
A=0 80% or more

Judging by Monday's dewpoints and 2m temps I'd go for a 40-60% in that instance.  For Friday's event A doesn't rise above 0 until midnight saturday down here in Southampton.

Someone with more knowledge may be able to clarify further though.

 

[icedust]

7 minutes ago, Quicksilver1989 said:

It would be extremely marginal for the north Midlands going by my rule of thumb. This is what I normally use as a quick guide:

Add together the Dew point and the temperature  = A
then if:-
If A > 7 prob. snow is very small
If A=7 prob. snow = 10%
A=6  20%
A=5 30%
A=4 40%
A=3 50%
A=2 60%
A=1 70%
A=0 80% or more

Judging by Monday's dewpoints and 2m temps I'd go for a 40-60% in that instance.  For Friday's event A doesn't rise above 0 until midnight saturday down here in Southampton.

Someone with more knowledge may be able to clarify further though.

That's a very interesting forecast tool. Not come across that before but it seems to have some physical sense, in that low dew points encourage cooling by evaporation, or sublimation, hence maintaining any snow that falls and reducing the melting into rain.  As a forecaster for many years one obviously had to consider the many variables that affect snow or rain to occur in the UK. The hardest one to get right is the intensity of precipitation. In marginal conditions this makes all the difference. Heavy snow cools air as it melts and falls further down before turning all to rain. So that is what usually embarrasses the professionals when unexpected heavy snow blocks roads. It was supposed to be rain/sleet but was so heavy it turned back to snow.  

So using your forecast tool above when say, A=40% the 60 occasions of rain, could be light to moderate ppn and the 40% when it snowed may be due (mainly, the usual caveats used in forecasting)  when it was heavy.

Also very difficult is the freezing rain scenario but the Americans have this more than us and will know all about that. I only came across it once in my 25 years as a forecaster and it was forecast well using model guidance with a good nose of above zero air at 900mb to 850mb.  For the end of the week, lets hope the professionals have some decent model output regarding that hazard nearer the time.

[Dominic Carey]

I'm hoping for a major turnaround to a continuation of cold

[Djdazzle]

At first glance GFS 6z looking better than 0z.

[MR EXTREMES]

Unfortunately there's no change from the 6z GFS, cool and wet beyond the weekend far north of England could hold on to the cold for couple more days but most UK wet and cool with rain.

So longevity cut short.

so fingers crossed for some showers here in the Portsmouth area.

Blocking zipping quickly through Greenland into the Eastern seaboard of the united states.

 

[MR EXTREMES]

By t150 the coldest air just touching the very north of Scotland.

So make the most of it as fair few months to next winter although net weather team done good this winter and I'm happy it was not a blowtorch winter.

Now fingers crossed the solar minimum flat lines for the rest of the year ready for next winter.

But there's no doubt away from the south coast over the next few days there alot to be excited about especially bit further inland as the models do suggest blizzard conditions over the next few days.

So definitely make the most of it.

 

[johnholmes]

Well the 500 mb anomaly charts now all 3 do suggest that there is no way back to the extreme upper air charts we have been seeing. The overall impression is for less cold after Friday to start to take over. Not mild but certainly less cold than most of us have been having over the last few days.

I made this comment for myself in my daily check of the anomaly charts

So overall this morning is by 8-10 days the weather will be less cold, (in fact from the weekend), and an increasing emphasis on the flow being from the atlantic area, still north not south of uk. No real sign yet for any marked spring like temperatures, some settled days some changeable ones, snow higher ground n Pennines north, and the charts as usual below

http://www.cpc.noaa.gov/products/predictions/814day/500mb.php

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

[johnholmes]

1 hour ago, Ruzzi said:

Ofcourse it is, there's no doubt about that... but for the past few days, it's practically all that's been spoken about and that'll be the case til the end of the week. Sorry, not wanting to be off topic or pedantic. It's just making for poorer reading for a lot of members when we have such a great set-up and week ahead 

Have you dipped into the other short term thread, that has plenty of posts about this week?

[stodge]

Morning all

Plenty of interest in the models this week and through the weekend and plenty still to be resolved in terms of the timing, duration and reach of any milder Atlantic air at this time.

I'm looking ahead to the end of next week which is Friday March 9th with my musings and as always kicking off with the ECM 00Z OP at this time:

A WNW'ly flow covers the British Isles with a ridge extending from the south over western parts. A complex trough sits to the east and north with a new LP moving up from the SW. A brief more settled spell of weather approaches but with uppers at -4, temperatures remain below average for most.

GEM 00Z OP at the same time:

Between areas of HP over Greenland and Scandinavia, a shallow complex trough covers north west Europe and out into the Atlantic. One LP centre over Eastern Europe and another far to the SW are bridged by a weak HP ridge from the south. The British Isles is in a calm set up but a weak N'ly covers eastern areas. Uppers remain well below zero (-4 to -8 generally) so temperatures remain on the cold side and wintry showers are possible with snow to altitude.

GFS 00Z OP at T+240:

A mild SW'ly flow covers the British Isles with LP to the west in the Atlantic and heights to the NE over Scandinavia. Areas of frontal rain and showers interspersed with drier brighter periods for all and temperatures above average. The unsettled theme continues through the rest of FI with areas of LP passing over the British isles bringing spells of rain and brief windy conditions.

GFS 00Z Control at T+240:

The British Isles is covered by a shallow but broad trough with a second LP centre to the SW. Light or calm conditions continue with uppers -4 generally so wintry showers for many with snow remaining a presence to altitude but rain at lower levels. Further into FI it remains unsettled but with the jet gradually shifting north it becomes milder.

The GEFS at T+240:

http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=240

Broad agreement on the dominance of the trough but some differences over positioning and orientation and I would argue a majority of members keep the British Isles on the cold side of the trough at this time. Yes there is a minority of milder solutions where the OP sits but the Control is perhaps more representative of the overall suite at this time.

In summary, whatever the twists and turns of the weekend, the battle between the cold and mild air-masses I alluded to yesterday continues. On balance, the cold air-mass remains in charge to the end of next week on most of the output though GFS OP (not surprisingly) is more progressive and goes much milder. The cold we are currently experiencing isn't on the agenda and neither is a settled regime with the trough very much in charge (indicative of MJO 2/3 perhaps and it might have been better had it gone into the CoD as seemed likely at one point). Heights continue to exist over Greenland and Scandinavia but the signals remain muted at this time. 

 

[Man With Beard]

ECM cluster report: No clusters after just T96 - Not because they are broken, but because they do not have a clue!!!!

I looked at individual ensemble members for D8/D9 on weather.us. Totally random!! In fact, the number of runs with minus 8C uppers or below probably outweigh the milder runs! 

The only pattern is low pressure very close to the UK, with a marked difference in coldness depending on whether the low is centred a few hundred miles west / east / south / north.

Little point, therefore, looking beyond the model mess of the end of this week IMO.

[nick sussex]

Looking at the trend of the outputs it’s very complicated .

What looks to be happening depending on which model you use is the first main band of snow associated with the low to the sw will work nw.

The latest Arpege has heavy snow from a line west Hants down into the sw towards Bristol and sw Wales and moving into se Ireland .

Thats associated with the main low, a front then straddles the Channel this then works its way slowly ne wards but is a weaker feature .

The problem is the models continue to disagree on where exactly the main low goes.

The depth of the low will also effect its track.

 

[john mac]

1 minute ago, nick sussex said:

Looking at the trend of the outputs it’s very complicated .

What looks to be happening depending on which model you use is the first main band of snow associated with the low to the sw will work nw.

The latest Arpege has heavy snow from a line west Hants down into the sw towards Bristol and sw Wales and moving into se Ireland .

Thats associated with the main low, a front then straddles the Channel this then works its way slowly ne wards but is a weaker feature .

The problem is the models continue to disagree on where exactly the main low goes.

The depth of the low will also effect its track.

 

It’s got nowcast written all over it nick.

[nick sussex]

Just now, john mac said:

It’s got nowcast written all over it nick.

Yes definitely , it’s turning into the Da Vinci Code low! 

Its a very unusual set up, normally breakdowns occur with the main jet heading towards the UK. So the models have to juggle the energy , how much goes ne versus se.

Theres no real drive behind the low the main jet is heading towards Africa .

 

[Snowy L]

11 minutes ago, nick sussex said:

Yes definitely , it’s turning into the Da Vinci Code low! 

Its a very unusual set up, normally breakdowns occur with the main jet heading towards the UK. So the models have to juggle the energy , how much goes ne versus se.

Theres no real drive behind the low the main jet is heading towards Africa .

 

That's what is so frustrating. The low has no backing from the jet yet it moves aside -15c air with the softest of nudges.