Model output discussion - The run up to Christmas

[syed2878]

1 hour ago, TSNWK said:

My thoughts if I may.. that this 06z is actually a slight upgrade from the 00z up to about 190.. it then starts a slightly different route where we have slightly more flabby low filling over us brining in less cold uppers to around 240 although we have gone back to a cut over Greenland high option...

Absolutly top draw model watching at present.

 totally agree fascinating model watching at the moment 2010 was I would say very similar although I am stand to be corrected however regarding any low-lying snow fall next week of the disruptive later I await Met offices update today before I get all excited. someone already said it I think snow or not the synoptic output from the models are fascinating this year to watch.

[Chesil View]

As others have said fascinating model watching, a million percent better than this time last year that’s for sure. Looking at the gfs ens in the longer term  several play with the idea of our friend the much maligned Russian high linking across the top towards Iceland /Greenland. Maybe a trend to watch out for in the longer term.

[Catacol]

2 hours ago, bluearmy said:

Twitter is a scary place .........

Gfs ops showed a split of the spv but we’re never consistent with post warming placement of the vortices. The split caused by a push across from the strat ridge the pacific side of the NH. We can expect one vortex to end up in n America and one Asian side. That could be as far to the east as e Canada/newfound and as far to the west as scandi. The envelope on that too far away to pin down. 
recent gfs ops have backed off from a split with most showing a stretched vortex at 10hpa by the end of the runs. But they would likely split beyond the end of the run. 
 

we don’t get to see eps extended strat data but some of the stuff on Twitter seems to show a similar picture to the more progressive gfs runs from a couple days ago with split across the pole within two weeks 

A few charts to reinforce what BA is saying here. I still like the slightly out of fashion Berlin plots... - but they are valuable because they are ECM driven and not GFS.

Vortex way up at 10hpa for NY Eve 

 

Note the extreme stretch of what should be a tight formation, and the high temperature flux firing in from the Asian side.

Lower down at 150hpa on the boundary between strat and trop, on NY Eve again, take a look at this sorry creature...

 

Ive rarely seen such an incoherent shape - and note the wind speed average has dropped to 5 m/s. Today at this level it is 17.

If we take a stretched vortex way up high and a very unsteady vortex down at the bottom we need to know what happens next. Ideally another bout of wave flux to turn that stretch into a split and shatter it for good. Using the more fashionable strat observe charts (GFS sourced) we can see significant wave flux up through the layers being fired poleward at the vortex on NY Eve once again

and if that chart is confusing the ECM Berlin product shows the same in a slightly different format

That ECM flux chart is huge. 
 

What does all this mean? That on NY Eve when we are all wanting to party and already stretched and wobbly vortex with much reduced wind speeds and incoherent shape is about to be hit by a major poleward heat arrow, fired into its core through multiple layers. If this was happening to a vortex that was still a coherent shape it would displace. But to a stretched and weakened formation? I can only see it shattering. This could well happen before the first week of January is out, looking at these charts, and from there the question is speed of downwelling impact. Given the current NH profile and dispensation to trop led blocking already we probably won’t feel an impact until the second half of January....but that impact will serve to weaken the Atlantic further, and if the split happens as we hope/think it might then we end up with a high lat ridge in the Atlantic centre - right over our heads. Trough energy inbound from the east.

If this all comes to pass then January starts fairly cold and over time probably gets colder. All this unless something changes - and if it does knowledgeable folk will flag it. For now keep enjoying the ride.....

 

 

Edited December 23, 2020 by Catacol

[Penicuikblizzard]

2 hours ago, Tim Bland said:

I suspect if truth be told some members don’t understand the differences between a Reversal, split & displacement. Key here is that there is more than likely going to be a SSW and the above are the possible outcomes of that warming. Some people panic when they hear a line from someone suggesting that one of the above isn’t going to happen ...it still (probably) means the SSW is on.  No need to sell the kids sledges..

if anyone has time over the Christmas period who fully understands the nuances and likely effects on the Uk weather of a Reversal, split & displacement it would be great if they could write a post as it would assist conversations and understanding going forward. 

p.s great to see media forecasts now showing the widespread snow potential next week. Looks similar to the ECM path...

Can you show me on this map where the widespread snowfall is ??

[winterof79]

1 hour ago, tight isobar said:

Synpoticaly stunning @6z gfs...    the uppers @850s are pointless viewing by now we are entrenched!!

Correct if/when the low fills we will develop our own cold pool as it slacken. Happened in 2009 streamers off the Irish sea? 

[feb1991blizzard]

3 hours ago, bluearmy said:

INCORRECT !!!!!!!!!!!!

please don’t mislead the forum ......

Where is the split??

EPS are a stonker though.

Edited December 23, 2020 by feb1991blizzard

[Kent Clipper]

Great time to have joined this forum. So much useful content being shared and discussed. 

[Penrith Snow]

Just to illustrate how milder uppers do not prevent snowfall. Uppers over Cumbria at the moment are about -1c but heavy rain turned to heavy snow over high ground this morning, settling above 1000feet and causing traffic problems on cross Pennine routes. No mention of high ground snow on any forecast. I suspect this scenario will be repeated much closer to sea level across the UK next week. Andy

[Tim Bland]

26 minutes ago, Penicuikblizzard said:

Can you show me on this map where the widespread snowfall is ??

If you want to see the video go to their Twitter page, this is just a screen shot of a video. it follows / displays the ECM run which gives this...

Edited December 23, 2020 by Tim Bland

[Penrith Snow]

3 minutes ago, Met4Cast said:

Great for the 25 people in the UK that live above 1,000 feet.. 

of course not many people affected, however, my point is if uppers of -1c can bring heavy snowfall above 1000 feet next weeks uppers of -5c could bring snowfall close to sea level given similar heavy precipitation and calm wind conditions.

[winterof79]

Let's face the fact if this sets up we're in the game at some point. You can worry all you want but this chart will deliver at some juncture. 

 

[northwestsnow]

13 minutes ago, Penrith Snow said:

Just to illustrate how milder uppers do not prevent snowfall. Uppers over Cumbria at the moment are about -1c but heavy rain turned to heavy snow over high ground this morning, settling above 1000feet and causing traffic problems on cross Pennine routes. No mention of high ground snow on any forecast. I suspect this scenario will be repeated much closer to sea level across the UK next week. Andy

Are you standing by the 1500feet snowline next week still ?

I'm thinking the Midlands down to the SE are going to get pummelled!

BTW,sorry Andy if I got you mixed up with someone else regarding the 1500 feet.

Looks to be trending colder to me ..

Fred, UKMO not far south enough with the trough at 144 ..

Edited December 23, 2020 by northwestsnow

[northwestsnow]

12 minutes ago, Tim Bland said:

If you want to see the video go to their Twitter page, this is just a screen shot of a video. it follows / displays the ECM run which gives this...

Goodness that graphic looks brilliant for the Midlands,and Shaky !!!!!!!!! !!!!!!!! !!!!!!!!!

EC chart says 38cm !!!!!

Incredible !!!!!

Edited December 23, 2020 by northwestsnow

[Catacol]

EPS mean for 10 days’ time. Don’t get many of these that look so meridional and favourable going forward. How long before the pattern backs easterly.....

[MATTWOLVES 3]

4 minutes ago, northwestsnow said:

Are you standing by the 1500feet snowline next week still ?

I'm thinking the Midlands down to the SE are going to get pummelled!

Stop it mate....my family just had to administer smelling salts for me to come around,when you said that. Surely not a December 2017 situation when the Midlands got pummelled. I can see alot of places getting a snow fix next week,very much going to be an evolving situation...we are all in the game.

 

[northwestsnow]

Just now, MATTWOLVES said:

Stop it mate....my family just had to administer smelling salts for me to come around,when you said that. Surely not a December 2017 situation when the Midlands got pummelled. I can see alot of places getting a snow fix next week,very much going to be an evolving situation...we are all in the game.

 

have you seen that BBC graphic mate?

OMG ...it matches the EC chart showing 30cm...

I'd be so excited if I lived in the Midlands!

[Winterdarkness]

11 minutes ago, winterof79 said:

Let's face the fact if this sets up we're in the game at some point. You can worry all you want but this chart will deliver at some juncture. 

 

Yep we are in for a 1978 winter 

[northwestsnow]

Metoffice automated now showing snow symbol in Birminham next tues!

Must go off EC ?

The trough is further south on EC hence I preffered it over UKMO ...

Edited December 23, 2020 by northwestsnow

[Kirkcaldy Weather]

2 minutes ago, Catacol said:

EPS mean for 10 days’ time. Don’t get many of these that look so meridional and favourable going forward. How long before the pattern backs easterly.....

Many positives continuing with the models such as .. 

[Jason M]

8 minutes ago, northwestsnow said:

Are you standing by the 1500feet snowline next week still ?

I'm thinking the Midlands down to the SE are going to get pummelled!

BTW,sorry Andy if I got you mixed up with someone else regarding the 1500 feet.

Looks to be trending colder to me ..

Fred, UKMO not far south enough with the trough at 144 ..

I'm getting very concerned about next week. There could be significant disruption due to snow in the more mountainous areas of the SE England & East Anglia. Just a shame that all the Suffolk Ski resorts are closed due to COVID restrictions .

Joking aside, the GEFS look in terms of cold or rather cold weather going forward. Given the synoptics it is surprising that we are consistently not seeing any rogue ensembles bring in sub -10c 850s later in FI.  

 

[radiohead]

GEM highlighting the potential for freezing rain at times next week :

 

[Met4Cast]

5 minutes ago, northwestsnow said:

Metoffice automated now showing snow symbol in Birminham next tues!

Must go off EC ?

The trough is further south on EC hence I preffered it over UKMO ...

MOGREPS I believe.. 

Re: BBC graphics, I wouldn't get too excited. BBC/Meteogroup use raw data at the extended forecast range which is why the BBC chart matches so perfectly with the EC det. In my opinion they've gone downhill since dropping the Met Office. 

Next week is looking interesting though.. because it's so marginal it wouldn't take much of a change to see a rain or snow event.

[Methuselah]

3 minutes ago, Winterdarkness said:

Yep we are in for a 1978 winter 

Personally, I'd like to see an exact copy of 1978-79's synoptics (utterly impossible I know!): I've always been fascinated by 'then and now' comparisons... But, just how similar would things have to be, for such a comparison to be meaningful?

But, be that as it may, the latest GEFS mean NHPs hold plenty of interest:

    

    

[Kentspur]

26 minutes ago, Tim Bland said:

If you want to see the video go to their Twitter page, this is just a screen shot of a video. it follows / displays the ECM run which gives this...

My only concern is for us in the SE corner and other Southern/Eastern areas that the M4 line will work its magic it looks like mainly rain for us on those graphics unless it transitions as it clears although the ECM charts people have been posting show accumulations even around London and surrounding areas

[Kasim Awan]

22 minutes ago, northwestsnow said:

Are you standing by the 1500feet snowline next week still ?

I'm thinking the Midlands down to the SE are going to get pummelled!

BTW,sorry Andy if I got you mixed up with someone else regarding the 1500 feet.

Looks to be trending colder to me ..

Fred, UKMO not far south enough with the trough at 144 ..

The snow line will reach sea level for a few places at some point 27th-29th.