Model output discussion - The run up to Christmas

[Kasim Awan]

The GFS is good. D7 to D9 we see an easterly develop which is, theoretically, a credible  possible outcome given the tendency for these ridges to pull away SSE. Also, higher heights are spawned to the NE connecting to the area E of Svalbard which seems juxtaposed to produce H pressure at present. This all promoting a temporary easterly.. This produces wintry surface conditions.

Next. The low diving SE from Greenland is also credible, given that there is a trend for amplification and a NW-SE jet prescribed nicely by the EC 00z op; this could well become cut off and run another attempt at an easterly around D10.

Edited December 22, 2020 by Kasim Awan

[LRD]

7 minutes ago, Geordiesnow said:

Not cold enough I'm afraid not with winds off the sea. 

It's is astonishing at the lack of cold on our part of the hemisphere, there is just no PV there at all! No wonder we are feeding on scraps. 

We always get winds off of the sea. We're an island 

[Matt H]

No westward shift on the GEM 12z either out to t150, looks similar to the GFS. Hopefully the ICON is isolated this evening.

[TSNWK]

If we can get this chappy from the north west just a smidge further east we would have a disrupting low with below -5 uppers bumping into us when the country is at least -6... dreams wistfully:)

also still looks a tad less amplified for the next phase of heights from the west.. hopefully this slight less sharp approach will mitigate west nao.

 

Edited December 22, 2020 by TSNWK

[The Northern Ramper]

1 minute ago, LRD said:

We always get winds off of the sea. We're an island 

You know that was almost as informative a post as Snowkings

[tight isobar]

Last 1 until later.. but we have classic deep jet synoptic.. so we can now start looking via- output.. for own cold pooling creations... which are susceptible in this classic set up... your 850 hpa anguish.. will I think soon be.. quashed...@keep watching!!

[Met4Cast]

Very subtle shift west at 126hrs on the GEFS which places the low over the UK, whilst we don't want to see a westward shift, the low OVER the UK and slowly filling like this would allow for evaporative cooling under the slack winds.

[MAF]

perhaps @LRD was meaning to describe the sea surface temps SST's which would make his post relevant and not worthy of dismissing as something irrelevant  

 

[Battleground Snow]

So close @Scott Ingham at 252

 

needs a little shift south east still, and keep Iberian heights low

 

 

[MAF]

i wish people would be not so dismissive of other posters. we are all here for a reason. and the weather is the main thing. 

 

[Daniel*]

Interestingly the 4th December which experienced some wintry weather even a covering in coastal Clacton has some extremely close similarities to upcoming pattern. It will be less marginal than that for sure...

[sheikhy]

Control and mean look fantastic!!low thicknesses slack air flow 850s of -4 or -5!!recipe for a lot of snow and really cold temps!!

[Kasim Awan]

Amazing GEM.

Surface Easterly then a "low of polar origins" about to dive SE.

[LRD]

5 minutes ago, MAF said:

perhaps @LRD was meaning to describe the sea surface temps SST's which would make his post relevant and not worthy of dismissing as something irrelevant  

 

Nah, I was taking the p

Fantastic synoptics in GFS FI but it's unvbelievable how little deep cold there is about. Probably won't need it in this scenario though

Edited December 22, 2020 by LRD

[tight isobar]

1 minute ago, Kasim Awan said:

Amazing GEM.

Surface Easterly then a "low of polar origins" about to dive SE.

cracking Canadian this evening.. @the America’s lead the way..

[kold weather]

Subtle shift past 180hrs makes the world of difference, the 12z GFS FI at least to 264hrs is looking very good for most of the country.

This is going to be a humbdinger of a FI.

PS - still a more than reasonable chance of a snbow event between 28-29th, though much depends on placement and strength of any secondary depressions. Too early to have any confidence beyond 27th.

Edited December 22, 2020 by kold weather

[NewEra21]

2 minutes ago, Kasim Awan said:

Amazing GEM.

Surface Easterly then a "low of polar origins" about to dive SE.

Yep, the GEM has been the pick of the bunch for the past few afternoons.

[Geordiesnow]

13 minutes ago, Frosty Winter said:

Have you read the excellent post from @snowking earlier about 850hpa temperatures and snowfall? Definitely worth a read as it provides a very good explanation about why uppers aren’t always necessarily the most important factor when it comes to snowfall. It was very informative as they don’t have to be as low as I initially thought for decent snowfall.

Yes and it's a very good post but when you got winds coming in from a warm north sea then there is much more mixing in the layers of the atmosphere so no good having - 6 uppers if the temperatures at lower levels are at 4C because of the warming affects of the North Sea. 

The best and perhaps only chance for snowfall is as the low heads through the UK and the winds fall slack and that is when the very low thicknesses come into play despite not very cold uppers but as soon as the wind increases then it will all turn back to rain at lower levels and most higher levels.

[TSNWK]

And that I think is what is called a negative nao and it ain’t west based either.. it looks a little feeble but we do have a cut off Greenland high I believe?
 

nice run.. bank! I’ll take my chances on uppers which for the best part are bouncing around -5 in south east.

 

 

 

 

Edited December 22, 2020 by TSNWK

[Met4Cast]

2 minutes ago, Kasim Awan said:

Amazing GEM.

Surface Easterly then a "low of polar origins" about to dive SE.

This shows how an Atlantic block is more than enough if we can get low heights diving into Europe. The ship for high latitude blocking has sailed now, at least in the first run of amplification, though quite possibly the second too, but that's still uncertain, but with low heights over S Europe it doesn't matter, there's no easy route to cold from that point & it prevents the Atlantic high from toppling.

[Kasim Awan]

I think there is a tendency for people to get overly dependent on the Numerical Model's first solution of how the cold will occur. The evolution is constantly changing, and the route to cold will evolve with each run. Good sign something is a foot because we are at least dealing with model attempting to resolve blocking outcome - this a sign a background factor is at work.

Edited December 22, 2020 by Kasim Awan

[feb1991blizzard]

6 minutes ago, Kasim Awan said:

Amazing GEM.

Surface Easterly then a "low of polar origins" about to dive SE.

Stonker yes - with uppers between -3c and -4c

[Kasim Awan]

1 minute ago, feb1991blizzard said:

Stonker yes - with uppers between -3c and -4c

Perfect for IMBY.

[Guest]

2 minutes ago, feb1991blizzard said:

Stonker yes - with uppers between -3c and -4c

Definitely the correct thing to focus on at t+168 

[Daniel*]

Where’s the isobars gone? This would be a very cold solution. Where you have snow cover, severe cold nights.