Model output discussion - into the start of Winter

[Mike Poole]

Looks like a direct hit from the north on the JMA T192:

Good 12z output today, confirms the view we are in the game, and probably will be for a few weeks if the strat and trop vortexes stay disconnected, actually getting more so on the NAM plot, based on todays GFS 0z:

Thereafter, the scene seems to be set for a possible SSW with the Aleutian low, Russian high combo, a significant precursor, so recurring in the output, illustrated on the ECM T240 chart:

With the start of winter only 4 days away, coldies could hardly have more irons in the fire, so to speak...

 

Edited November 27, 2020 by Mike Poole

[northwestsnow]

Agreed Mike...

There has been an abundance of blocking to the NE this November...

Could we see a SSW later in December??

I referenced this block earlier, at 1050mb its a monster ...

[Daniel*]

33 minutes ago, Jon Snow said:

I’ve run out of reactions..shame cos there’s some great posts again today..anyway, looking at the the ECM 12z op..at least it isn’t mild judging by these uppers (850’s)...and there is scope for something much colder..with a bit of luck!..sorry charts not in order, I’m as drunk as a  

Yep it’s chilly very wet on Friday but turns to snow in night in capital we can dream

 

[damianslaw]

Very interesting synoptics at present, models forecasting the longwave trough dropping right through the UK, not often this happens. Locked in place by mid-atlantic heights and strong heights to our NE. Crucially we end up with much lower heights over S Europe, a NW-SE trough alignment. Had we more of a cold pool ahead of the trough and wrapped within then some significant wintry precipitation would be on the cards, alas looks like any wintry stuff will be reserved for places with height further north, but certainly fine margins and evaporative cooling could produce some low level surprises.

Longer term - may see a repeated attempt at more substantive colder air from the north.

[stodge]

Evening all

For a change tonight, not reading anyone else's contributions (invaluable as they no doubt are) and ploughing straight into the output:

GEM - pretty decent for cold weather fans with clear negative alignment of the trough which sinks SE over or just to the west of the British Isles. The blow from T+168, T+228 and T+240

All FI of course but the wedge of heights across Scandinavia and toward Iceland holds increasingly frigid air and that "block", insubstantial as it seems, is enough to send the LP away SE and with a renewed pulse of WAA over western Greenland, will we see the Mid-Atlantic ridge develop?

GFS - OP

The 06Z OP backed off disrupting the trough through the British Isles completely so what does the 12Z OP offer? Well, disruption is back to a point - at T+168 we see the trough elongating into a shallow but extensive feature running north through the British Isles from a main centre close to southern England. By T+204 the LP has developed into a classic "Genoa Low" with heights starting to build in response over Scandinavia and that block forces the next trough to align negatively and dive SE across Ireland at T+240 so not a million miles from the GEM above at the same point. From there, an element of traditional GFS re-set kicks on but there's no long-fetch SW'lies and a raging jet on offer. Indeed, the trough continues to align negatively. I'll conclude with the T+384 NH overview and simply say I've seen a lot worse for mid-December.

ECM - will this be the fly in our soup or the cream on the cake?  First thing is to get the LP and trough to disrupt down over the British Isles and at T+168 we have something that aligns nearer to GEM than GFS but would bring a nice bit of cold rain for many - 850s are 0 to -4 so I'll yield to the experts on dew points and the like but there should be something wintry for high ground you'd think.  The trough never quite disrupts fully and becomes a complex feature and though there is a defined centre over Europe it's the one to the west of the British Isles which develops as the next significant LP and moves in by T+240. It draws in milder air from the south-west. The two routes for the LP are NE or SE. The other concern for cold weather fans is the PV energy seems to be leaking back across the Pole to northern Canada. This is a typical response to a warming from the Siberian side - I'll be honest, I'm really worried the warming will allow the Strat and Trop coupling to occur and it will be game over for the bulk of midwinter but I hope I'm wrong.

GFS has backed off the warming a little but it's a real worry and emphatically NOT what we want to see - if it were from the Canadian side that would be different but they are as rare as hen's teeth.

In conclusion, looking like a chilly and unsettled start to December and we could be looking at an extended period of negative trough alignment which would be good news for fans of snow especially in the north and east. We need to see the block develop and hold over Scandinavia and what we don't want is anything to send the PV back over to the Canadian side which would fire up the jet, smash the block and reset the pattern to something with which we have had to become accustomed too often in recent years (though I suspect it's been the default pattern for millennia).

 

[snowsummer]

22 hours ago, Met4Cast said:

A few members from the latest EC46 Zonal forecast going for a major SSW in late Dec/early Jan.. 

Is this the same one that @snow lover2020 mentioned earlier?!!

[Mike Poole]

ECM mean T240:

Noteworthy are the Southern Europe trough, the position of the vortex, way displaced from Greenland, Canada, and the Aleutian low, Russian high, as mentioned earlier.  

[feb1991blizzard]

53 minutes ago, swfc said:

It is NW, going north

We need it to do a pet shop boys.

[weirpig]

Maybe I'm off on one  and slightly drunk   but  a tad further east  and we could be looking at copious amounts of snow    for certain areas    at least its interesting 

[bluearmy]

Couple of ec comments 

1) ec op is in the smallest cluster in the day 5-8 period  - 10% 

Number of clusters at day 8 = 5

Number of clusters at day 10 = 3

number of clusters post day 10 = 1 ........ yeah, sure !

best to just keep watching awaiting some better guidance re the low trough placement ....

 

[sheikhy]

13 minutes ago, bluearmy said:

Couple of ec comments 

1) ec op is in the smallest cluster in the day 5-8 period  - 10% 

Number of clusters at day 8 = 5

Number of clusters at day 10 = 3

number of clusters post day 10 = 1 ........ yeah, sure !

best to just keep watching awaiting some better guidance re the low trough placement ....

 

How is the larger cluster looking mate!!better than the op days 5-8?

[matty40s]

42 minutes ago, weirpig said:

Maybe I'm off on one  and slightly drunk   but  a tad further east  and we could be looking at copious amounts of snow    for certain areas    at least its interesting 

It'll all end in tiers.

 

 

[Froze were the Days]

1 hour ago, northwestsnow said:

We need that whopping 1050mb high across NW Russia to make a move...

Problem is once again we're seeing some form of a jet stream or low pressure wanting to keep forming in the Norwegian to Barents Sea vicinity (something which has been apparent the last few weeks or so).

[bluearmy]

13 minutes ago, sheikhy said:

How is the larger cluster looking mate!!better than the op days 5-8?

Hard  to tell ..... and low confidence re continuity run to run .....best wait ...

[Mike Poole]

ICON 18z, T120 compared with T126 from 12z:

Increased separation of those two lows out west from the main vortex (good), similar in our neck of the woods...

[ALL ABOARD]

GFS better at 114 with the ridge. 

 

Up she goes?? 

 

[Matt H]

Just now, ALL ABOARD said:

GFS better at 114 with the ridge. 

 

Up she goes?? 

 

Yep looks better so far out to t120. Never underestimate the ability of the GFS to mess things up though.

[Griff]

Hmm  

[Mike Poole]

3 minutes ago, ALL ABOARD said:

GFS better at 114 with the ridge. 

 

Up she goes?? 

 

Yes, here T126 v 12z T132:

Sharper, and more push on the vortex to STAY AWAY too!

[Uncertainty]

This day 10 GEPS chart is givin me the creeps! Good continuity with an improved 12z EPS though...

 

Here’s the GEFS at the same time

Certainly making less of those mid Atlantic heights and no hint of a link up between that and the Urals feature. But given the 12z UKMO at day 7 was far more keen on the more amplified solution then given the ECM/GEM trends then that still has to be the favoured solution. 
 

It’s a tough one though because this evolution doesn’t happen often, especially at this precise time of year. We have to acknowledge that evolutions like the GfS 6z will always be possible because it so often happens that way. Equally possible but still unlikely is a perfect disruption of the trough neatly to the south east with significant ridging to the NW replacing it, bringing wintry weather. The ECM op option of blowing up the trough is odd but can’t be discounted as it has been shown in varying forms for 3 runs in a row. Finally a half way house, potentially shown by the 12z GEM is also well supported. If one could ‘cash out’ with the weather (would be awesome) then would you take this chart at day 10?

 

 

Edited November 27, 2020 by Uncertainy

[SMU]

GFS has now got the pattern expected spot on -96-144 but is still finding room to amplify the jet & make the cut off points more acute.

As a result that lows line of travel at 120 is almost due south, - So a retraction west on the 18z means its going to mostly slide west of the UK.

Upstream amplification better -

Edited November 27, 2020 by Steve Murr

[Griff]

Looking for Iceland (not the supermarket) 

[Eskimo]

Could be some snowy surprises even though upper temps aren't particularly favourable, with the winds being as light as they are in the chart below.

Edited November 27, 2020 by PerfectStorm

[Griff]

A wise man said the trend is your.... 

[SMU]

I think 99% of people would bank that chart given the choice.

Very cold & seasonal especially for Scotland...