Model output discussion - here comes the beast!

[Derecho]

3 minutes ago, Kentish Snowman said:

That GEM run has cold uppers over the Northern half of the UK right out to day 10 so I wouldn't say no going back (if you are talking about the cold pattern generally)?

Yup, I think an unsettled pattern with milder uppers making their way across the whole of the UK eventually. There would need to be a big rise in pressure over Scandinavia to keep us in some cold air. Quite a way off though at this point.

For Friday's snow event I'd rate them as follows for the south.

GFS - Especially snowy with it all falling as snow, except for the far south perhaps for a short time.

UKMO - Colder uppers but the surface cold is placed further north. Would be snowy for the Midlands but I think snow would turn to rain in the south

GEM - Snow initially then turning to rain before the chance of snow later, too messy though

ICON - Snow to rain to snow in the far south, snow elsewhere but a much shallower low.

Anyway to underline what a knife edge scenario this is, the 12z ensembles are actually a notable improvement with regards to Friday's low down here.



P1 is an example of what I wish to see 

[Steve C]

1 hour ago, Captain Shortwave said:

Day 6 from the GFS

GFS probably good enough with the low stalling just short of the UK and starting crawl east along the English channel, whilst 850s lift out it is still good enough for snow.

UKMO

This does bring a more maritime feed into the south though a spell of heavy snow is likely with it turning back to rain on the back edge, not overally mild behind, just less cold. We may get the colder air back south again though with that cold air extending east.

GEM

SImilar, heavy snow turning back to rain on the back edge, never overly mild afterwards with the cold air never far away in the south and never really leaving the north.

The theme is similar in terms of the broad trend, but the placement of the pattern by a couple of hundred miles north or south is crucial in determining cold and snowy conditions on milder conditions. Plenty of precipitation moving across the UK given the set up which could easily turn to snow the further north you are.

 

How does such a reasonable assessment get so few up votes, compared to the not knowing their a*se from their elbow contributors who plague this thread with one liners/ sound bites? Needs properly sorting IMO. 

Edited February 24, 2018 by Steve C

[kold weather]

12z GFS ensembles seem to have slightly shifted the frontal shield on average further south and more runs seems to take the LP on a more easterly track meaning not as far north and no marginality for the south.Still a few runs that strike the perfect balance between the milder air mixing in and as much of the country getting the precip as possible.

[Frosty.]

Just been through the GEFS 12z and there is plenty of support for most or all of the uk to still be in the freezer by T+192 hours (sunday)..there are some strong reloads from the NE and only a few milder solutions like the op..could have been a lot worse but the majority keep the uk locked in either cold or very cold air with further snow!

Edited February 24, 2018 by Frosty.

[Penicuikblizzard]

Looking like a snow filled week for the North going by the 12zs ??

[CK1981]

3 minutes ago, kold weather said:

12z GFS ensembles seem to have slightly shifted the frontal shield on average further south and more runs seems to take the LP on a more easterly track meaning not as far north and no marginality for the south.Still a few runs that strike the perfect balance between the milder air mixing in and as much of the country getting the precip as possible.

I think this trend will continue as we progress through the week. My punt is the low pressure centre moving south of the Channel Islands and ENE through the Cherbourg peninsular.

I wouldn’t be surprised to see it further south though.

Edited February 24, 2018 by CK1981

[ukpaul]

GEFS brings the warmer uppers further north after 192h, looking at the mean it would seem that more members are bringing in the Atlantic via that second system. Again, if the first one could be pushed into Europe it would improve our long term prospects considerably.

[Summer Sun]

Short ens gives London 4 day's of sub -10 850's we then see an increase to around -5

 

[LRD]

I am not a massive fan of the GFS but if Friday does become a snow-rain event for the south, followed by a warmer wash out after that, kudos to it. It was the first to start pushing that low too close to us for comfort

Let's see what ECM says but UKMO has also moved and trended towards the low-moving-very-close to us option

[CanadaAl]

Just now, Summer Sun said:

Short ens gives London 4 day's of sub -10 850's we then see an increase to around -5

 

Encouraging to see the GFS op being a potential mild outlier

[ukpaul]

Still keeping a number of members in the colder air up north until Monday 5th, then a clear split but it does show that the warmup is a 50/50 chance.

This is for my locality and the op is the lime green line that goes depressingly high on Sunday 4th.

[CK1981]

2 minutes ago, CanadaAl said:

Encouraging to see the GFS op being a potential mild outlier

The colder cluster at that range has definitely increased over the past few days. A good trend for us all.

[Frosty.]

Next week's freeze is in the bag, let's be happy about that!..the Ecm 00z prolonged the cold potentially way past day 10..let's hope the 12z does likewise!

[Tom Jarvis]

@nick sussex nick would pert 16 be the likely track of the low based on your exsperience of how these thing go? 

[garylaverick]

An incredibly persistent period of snow being modelled for the NE, unlike anything I've seen before.

[Summer Sun]

12z mean looks to have gone up slightly compared to the 06z lots of scatter beyond the end of next week but the trend from GFS at present is to something less cold for the south at least

12z

06z

[khodds]

I don’t teally know or understand what all the fuss with GFS is about. Haven’t we been told that the Meto side with UKMO and ECM anyway? It’s still ages away; a lot could happen between now and then.

[Nick123]

2 minutes ago, garylaverick said:

An incredibly persistent period of snow being modelled for the NE, unlike anything I've seen before.

I don't see it on that chart?

[Summer Sun]

Just now, Nick123 said:

I don't see it on that chart?

It is a GIF click to play it

[karlos1983]

Just now, Nick123 said:

I don't see it on that chart?

Press it, it’s a GIF. I wondered at first lol

[ukpaul]

2 minutes ago, Tom Jarvis said:

@nick sussex nick would pert 16 be the likely track of the low based on your exsperience of how these thing go? 

PTB 16 is pretty much the perfect way of developing it - moves to our East, skims up the East coast meaning snow for all and doesn't mix out the colder air. Not only that the next system is barely developed.

Being the best possible solution you can guess the odds of it happening.....

[EML Network]

38 minutes ago, Singularity said:

 

Well this from UKMO would have serious impacts on our infrastructure.

Very telling I think that it takes the LP on a very similar track to GFS, but squashes it more against the cold air, with the warm sector being ejected more east leaving pretty much all areas with sufficient parameters for cold.

While there would be more of a maritime flow on the SE flank, this would be over deep lying snow and so greatly modified once a mile or two inland. With the uppers staying low enough and the very low dewpoint air being ingested, I can't see any reason why it wouldn't all be snow from that event.

 

38 minutes ago, Quicksilver1989 said:

Complex synoptic pattern for later next week now developing, I thought I'd go through each step of the interesting 12z run from the GFS. We seem to now suddenly have a very unsettled Thursday/ Friday coming up, so why is that the case?

Well Wednesday's developments are pretty important, ironically the easterly is too clean and the unstable air makes it all the way across the UK and into the Atlantic.


On Thursday the cold unstable air starts getting wrapped into the Azores low meaning it intensifies and mild air from the Med/ Africa starts moving northwards (left panel). The Greenland heights face towards the N. American side too much and cannot stifle the northwards progress of the low. However tiny changes can still keep the UK firmly embedded in the cold.

 

Finally here is a chart from January 2013 which shows uppers around -2C for Wales yet this was an area covered under a red snow warning and saw a pretty big fall! Shows if the cold surface air is in place then snow can still be achieved.



In the GFS 12z, the UK is still in the continental air come Friday

 All falls as snow, perhaps a few more borderline moments in the extreme south

Whereas the UKMO mixes in some Atlantic air, despite the colder uppers, more areas would see rain.

 Not as good, with continental air pushed north

The scope for a historic snowfall event is there but its a high risk game and with the GEM there would be no going back. So those who don't fare well from the easterly this week will be disappointed. However there is huge uncertainty about this period at the moment. Very impressive synoptics though, so enjoy!

So which is it ? 2 experienced posters on here giving conflicting opinions regarding the chances of an all snow event in Southern England or a mostly rain event at the end of the week. 

 

Having run through all the GFS runs (again) I can see that there is much more of a cluster than before going for a more southerly route with the centre of the LP going through Belgium(ish), I'm feeling a little more upbeat after seeing the following runs in the GFS 12z suite and I hope that this ''trend'' continues on following runs, I might have been a little too eager to throw my toys out of the pram...we'll see.

 

Peturbation 1

 
No 3

No 7

No 8

No 9

No 10

No 13

No 15

No 16

No 20

So that's 50% of the peturbations taking the low through northern France and NOT STALLING and retrogressing slightly West and North into the UK ala the Op and Control run. 

 

A significant number, the Uppers only tell half the story. 

 

 

[Nick123]

1 minute ago, Summer Sun said:

It is a GIF click to play it

Ok now I do ?

[Bristawl Si]

It's only a few days ago that confidence was high for a 2-week bitterly cold spell starting from tomorrow. Is that in the balance now?

GFS started a trend? Yday Ecm and ukmo had the low barely affecting UK; today's runs show they've moved the LP for end of next week north (compared to yday). GFS today also moves it further north (compared to its runs yday).

Interesting few days coming up, for sure.

[Snowmaggedon]

6 minutes ago, garylaverick said:

An incredibly persistent period of snow being modelled for the NE, unlike anything I've seen before.

North East England potentially going to bear the brunt off the Beasterly by the looks of it.