Model output discussion - Closing in on Christmas

[Decemberof2010]

Anybody seen p24 on the GEFS our at 384h?

It’s a STONKER

 

[Nick F]

I'm resisting to throw caution to the wind on potential between Xmas and New Year, looks nice from the 12z runs of GFS, EC and GEM, but can we trust them with how they handle the breakaway vortex heading from Greenland to Europe?

Already Xmas day has gone from cold northerly to mild northwesterly on GFS, some spots may even reach double figures east of high ground. With the breakaway trop vortex heading SE, ideally don't want it to grind to halt over the UK, or too far west. Moving SE or S best into mainland Europe best - but we need ridging to build to the north at the same time, not a trough extension from Greenland.

 

Edited December 18, 2020 by Nick F

[BlueHedgehog074]

Just to illustrate the drama a few spoke of regarding the models are making of that Low to the South-West, this is what various operational 12Z models are showing between 96 and 120 hours:

GFS

ECMWF

UKMO

GEM

ICON

NAVGEM

 

ECMWF, GEM, ICON and the NAVGEM have that main little Low to the South-West of the UK heading North-Eastwards to sit over us at 120 hours. Blows up as it does so, which would bring some stormy and wet conditions over the UK. Maybe some blizzards over the Northern UK mountains. The Low joins to the South of the bigger more general Low Pressure to the North/North-East of the UK. NAVGEM the most eager at 120 hours getting that little menace to the East of the UK pulling down a Northerly over us. 

On both the UKMO and GFS, the little South-Western UK Low fails to link up with the North and North-Eastern UK Low Pressure. Gets stuck underneath the Atlantic ridge. In fact, it looks like on the GFS the Low just fills and seemingly fades into nothing. Perhaps with anything left of it getting absorbed by the very shallow upper trough underneath the Atlantic High. As such, both the UKMO and GFS allow quite a clean flow to take over on the Eastern flank on the Atlantic ridge from the North-West over the UK.

As a matter of fact, the models that tend to have that little Low affecting the UK and merging it with Low Pressure further North generally have the Low a little more closer to the UK at 96 hours than the ones where the Low doesn’t. This is particularly noticeable on both the GEM and ECMWF runs where the Northern tip of the Low touches the South-Western Ireland coast. Maybe also worth noting is that the NAVGEM, ICON and, again, especially the GEM and ECMWF overall allow more of a space between the Atlantic ridge to our West and the European High to our South-East for the little Low to get caught up in the Jet to drag it up towards the UK.

The GFS and UKMO already give that impression that the little Low is going to get stuck with the Atlantic ridge feeling as though it is exerting more influence on that Low. The Western UK ridge being eager to lean over the top of it. Plus the fact that the Low on those two models is accompanied by a more shallower and cut off upper trough to our South-West. The Low on those 2 models just seems generally less developed than on the other operational models at 96 hours.

One last thing to note is that both the GFS and UKMO have the Atlantic ridge a bit closer to the East of the UK. Where as on the other models, the ridging appears to be a little held back further West thanks to that small Low slowing the Atlantic ridge’s Eastwards progression a bit. However, this does vary a bit depending which operational models you’re viewing. 

Even though the overall pattern is the most important, the above shows how there is uncertainty with smaller details in the nearer time-frames, particularly such as that Azores/South-Western UK Low. Some of this having some affect on the amplification of the ridge in the Atlantic. And as well as events further upstream, how long it may take for the ridge to topple. Still looking like a transient affair towards Christmas. But some monstrous amplification developing out West after that likely initial topple could provide something even colder and wintry between the North-West and East (charming 12Z ECMWF by the way ). Too far out for this to be guaranteed, although there is some pretty good support for it currently. 

Edited December 18, 2020 by DiagonalRedLine
Typo

[Mike Poole]

ECM mean and spread T240:

Very good.  And the uncertainty on the spread chart is now twofold, probably related to heights at the tip of Greenland, but more related to the low pressure across the UK related to the (hopefully) snow storm.  

We’re getting closer. 

Edited December 18, 2020 by Mike Poole

[Kentspur]

And to my surprise ECM 12z op isn't an outlier at all its well within the ensemble spread most days including at day 10!! Could this be happening?...

Edited December 18, 2020 by Kentspur

[Jeremy Shockey]

ECM 12 z Ensemble mean

Very encouraging for Christmas Eve and Christmas Day .......afterwards still likely cold but some uncertainty

[goosey007]

Remind me Gents when was last time/winter we have seen charts like this with some sort of level of consistency in FI or perhaps fair to say coming into the medium term ....?? 

[phil nw.]

A cold Christmas followed by a NH pattern promising a prolonged cold spell,what more could Winter lovers wish for?

Yes signs now that a chunk of the vortex is going to transfer across our north towards Scandinavia in the mid-term as we see a second amplification upstream post Christmas.

GEFS mean day 10

Both suites have the same idea just slight variations on the ridging,Obviously it would be good to see it drive as far north as possible to swing that cold to the ne more directly our way.

I wouldn't be concerned with snow chances yet.Let's see this pattern firm up and get the cold established then we can start to see where the surface features develop.

What a nice change to see these charts now where we have plenty of time to get the best out of this developing cold setup.

[Uncertainty]

2 minutes ago, Kentspur said:

And to my surprise ECM 12z op isn't an outlier at all its well within the spread!! Could this be happening?...

Yes the mean is sharper with the amplification and edging closer to N than W with the flow. I’ll report on the indv members soon, it’ll be interesting to see how many evolve like the op at day 9/10. Not too many, given the spreads. But evidently many of them go cold and stay cold.

Latter stages of the GEFS show no let up in the inverted climatology pressure pattern.

Ural blocking, high to the NW and the jet into the Med. GEPS is broadly similar but not as strong anomalies. 
Looks like an April chart

[BLAST FROM THE PAST]

1 hour ago, Weathizard said:

Just the small differences at 168

ECM MUCH better

 

BFTP

[seabreeze86]

17 minutes ago, Decemberof2010 said:

Anybody seen p24 on the GEFS our at 384h?

It’s a STONKER

 

Yeah I saw that it’s mental 

[BLAST FROM THE PAST]

Roger J Smith  6,768

Posted 12 hours ago

The uppers on the day 10 ECM panel appear a bit reluctant to follow the surface evolution, but if all elements further north phased in a little faster, that would be quite a dynamic change to the pattern locking in a very cold northeast flow from a rapidly building north Scandinavian block. The unseen day 11 and day 12 of that ECM run would probably look very frigid indeed. 
 

 

This is a post from RJS earlier today...now look at ECM 12z

*note the bold print
 

BFTP

 

Edited December 18, 2020 by BLAST FROM THE PAST

[Mike Poole]

ECM clusters T192-T240, there are 6 of them!

But I’d take all but the last, least probable one!

[Frosty.]

You can count recent cold christmases on the finger of 1 finger..but I think we will add to that this year according to tonight’s ECM 12z ensemble mean!..and whisper it but I think between crimbo / new year could deliver something even more wintry..watch this space! 

[BlueHedgehog074]

2 minutes ago, Mike Poole said:

ECM clusters T192-T240, there are 6 of them!

But I’d take all but the last, least probable one!

A lot of them seem to continue showing some troughing to the South or East of us over mainland Europe. A good number with the Atlantic ridges and also the big ridge towards our North-East over Siberia. Nice to see 

[Harsh Climate]

Can't believe what I'm seeing, 36 hours ago It looked like the writing was on the wall for endless mild zonality with the occasional cool snap mixed in. I wake up this morning and not only have the models made a full 180' turn, we only have on offer the number 1, crem de la crem winter set-up possible for the UK, a GREENLAND HIGH!!  . And now later in the day the ECM and UKMO have somewhat followed suit.  

As Van Tam would say, 'The train is now in sight! We still have a long way to go, but this is a good place to start.'

And regarding looking at any specifics this early I wouldn't bother, the main thing is once we get a greenland high, that guarantees prolonged locked in cold and snow chances for all! Providing it isn't a west based NAO of coarse  .

So things to watch:

1.WAA heading up western side of greenland

2.Greenland high develops

3.WE don't end up with west based NAO.

Then I say wax ya sledges, the snows a coming!! 

Edited December 18, 2020 by Harsh Climate

[Mike Poole]

Just catching up with posts, was on a zoom beer session with mates, but managed to sneak a few posts on the ECM anyway!  

I think there is a reason why some tempting model output in the day 10 region goes up in smoke, and that is that it runs out of momentum and proves to be wrong.  This spell has all the hallmarks of something that is now increasingly predicted  by the models, it is gathering momentum, and while we don’t know yet how it will affect our small country, it is sure as hell going to be fun finding out!  

Just a point of note, the GFS 12z has absolutely marmalized the strat vortex, and it is a split not a displacement:

I’m unsure of what that means for the longer term as i have explained earlier, but one thing is for sure, this and the trop developments are part of the same package, so whether the split enhances or reduces cold potential later, it is what it is, this is 2020-21 winter, right now.  

[phil nw.]

Just out of interest i noticed the chances of a colder turn just before Christmas on the combined  ens temp graph and mean charts this time last week.

and they have been pretty steady since.Day by day extending the below average trend.This from today's 00z runs

For anyone new to our hobby these give a quick at-glance guide to what to expect at the surface and illustrates any outlier operational runs.

link

Weather: Ensemble forecast

WWW.WEATHERCAST.CO.UK

---

Ensemble forecasts identify the expected spread of weather conditions and assess the probability of particular events

On that page you can also see rainfall and wind graphs too along with an explanation of how to read them,for anyone not familiar with these.

A useful quick reference guide i think.

 

 

Edited December 18, 2020 by phil nw.

[stodge]

Evening all

Christmas looms on the horizon but looking (unexpectedly) at a longer-range forecast on the BBC News Channel this afternoon, what interested me was the post-Christmas evolution and the LP dropping through the British Isles (perhaps) rather than Scandinavia. We'll see - a cold, crisp Christmas Day looks the form horse but perhaps the evening output now has other ideas.

12Z GEM - T+120 takes us to midday on Wednesday, the day before Christmas Eve and it looks bleak with an LP over the British isles and rain for many with some strong winds to the west and north of the storm centre. A ridge waits upstream. Oddly enough, the small LP exits more to the south east but a calmer Christmas Day is followed by the onset of a new Atlantic LP which deepens close to Iceland by T+180. The large Atlantic HP has eased slightly and the possibility of negative trough alignment is very much there.  Indeed, the trough drops SE over to just to the east of the British isles and on its western flank a potent N'ly sets up by T+240. The evolution from there is open to question - I don't expect full amplification to the stage of an omega block - there are signs of shortwaves developing but it's a fair push of warmer air and heights into Greenland so we'll see.

12Z GFS OP - an exciting opening from GEM but they've been an outlier before so feet very much on the ground for now. Indeed, some differences as early as T+120 on the GFS which, instead of having the LP over the British Isles, has already introduced a PM airflow. The LP never makes it to the country fizzling in the south west approaches. The ridge is building in but the Atlantic is starting to gather. The T+180 GFS chart is more progressive - I suspect because we've not had the LP sit over us and then exit delaying the ridge moving in. GFS sends the deepening LP toward Norway with heights building back north west toward Greenland from the HP. While I wouldn't call it a mild NW'ly, the truth is the 850s aren't impressive at this time for cold fans but as we know that can quickly change. The two HP cells join over Greenland and with the trough dropping into Scandinavia, the T+240 GFS chart is a cold weather fan's delight, albeit 72 hours late for Christmas. Minus 8 850s for the British isles wit the really cold air sitting out to the west.  From there, the Greenland HP quickly breaks down but the LP core moves into Europe and the British isles stays on the very cold side of the trough with the cold air staying in situ to end the year. From there, it becomes a nirvana for southern snow fans as we get what I could call a "reverse Channel Low" - that's to say ab LP forms over the Netherlands and runs south west into the Channel. Needless to say, that would be a real snow storm for the south - we don't argue margins in early January with -4 to -8 uppers. The run ends cold with heights building to the north but it remains to be seen if we can squeeze much more out of the spell. 

12Z ECM - a phenomenal GFS OP for cold fans, likely an outlier. Were it to verify, serious snow fall for London and the south-east. Enough drooling and dribbling - it's all far FI and won't verify. On then to ECM - will it be a hell raiser or a damp squib? ECM goes the GEM route to T+120 (as you might expect and it's what the BBC forecast suggested earlier).  By Boxing Day (T+192), the deepening LP is bearing down on us from the north-west (again as per the BBC forecast) but looks to be heading straight for us rather than for Norway. That's pretty much what happens - the LP drops pretty cleanly through the British isles to France and draws in an ESE'ly flow. Colder air on the northern flank of the storm and with -8 uppers crossing a relatively warm North Sea, are we looking at our version of "Lake Effect", which is what has happened in Japan where cold air has crossed the Sea of Japan (relatively warm) and dumped feet of snow on Japan.

Even more drama as the 12Z GFS OP splits the PV at 10 HPA which would be in itself extraordinary. To dampen the mood very slightly, 12Z Control ends anticyclonic but still chilly.

Conclusion - what a way to end the week !! Spectacular output for cold fans with cold blasts forecast from either the north (GEM and GFS), the North East (GFS OP FI) or the East (ECM). That being said, we've been here before and we've been let down so often before caution remains very much the watch word. The most exciting chart for me tonight is the 10 HPA on GFS OP which shows a split in January which would offer the possibility (but NOT the certainty) of prolonged cold. 

For now, the behaviour of the post-Christmas storm looks the key - does it head into Scandinavia and pull down a N'ly or drop through the British Isles and draw in an E'ly? Heads we win, tails we don't lose looks the answer - the BBC forecast was tending to ECM this evening but it's all still to be resolved. 12Z Control shows it could go less well so caution, caution, caution would be the three watch words this evening (well, it's the same watchword but you know what I mean).

[sebastiaan1973]

Oper and control are together on the winter path.

[carinthian]

With all the excitement of cold weather coming as shown some way off still on the day 10 charts, there is a little matter of whats to happen in the shorter term. The ECM chart below at 120 t shows a deep low  crossing the heart of the British Isles which would produce a lot of rain and possible snow to the mountains. There is a difference at this stage between ECM and that shown by GFS and UKMO  with the track and positioning of the low.. However, all models show a clearance by Christmas Eve into Christmas Day ,

C

[Scott Ingham]

7 minutes ago, Mike Poole said:

Just catching up with posts, was on a zoom beer session with mates, but managed to sneak a few posts on the ECM anyway!  

I think there is a reason why some tempting model output in the day 10 region goes up in smoke, and that is that it runs out of momentum and proves to be wrong.  This spell has all the hallmarks of something that is now increasingly predicted  by the models, it is gathering momentum, and while we don’t know yet how it will affect our small country, it is sure as hell going to be fun finding out!  

Just a point of note, the GFS 12z has absolutely marmalized the strat vortex, and it is a split not a displacement:

I’m unsure of what that means for the longer term as i have explained earlier, but one thing is for sure, this and the trop developments are part of the same package, so whether the split enhances or reduces cold potential later, it is what it is, this is 2020-21 winter, right now.  

Still too early to work out tur pieces but i love the look at where that warmth is on the strat chart. Straight through the middle of Greenland and Scandinavia. It leaves less chance of us evolving west based nao which brings with it chance of moisture from southerh tracking lows into february

[Methuselah]

Better things are on their way: 

 

Sure beats the last few years:    If it happens!

[Captain Shortwave]

ECM end day 6/8/10

 

 

 

Neatly shows the progress beyond Christmas Day. So we are likely to see a deep low run over the top of the Atlantic ridge before the trough east/ridge west of the U.K. is restored. No point getting too hung up yet but the general consensus after the next few days is for temperatures to fall a little below normal and this may be enough for some wintry precipitation at times.   

As for the big day, the GFS looks the fastest at being cloud and rain off the Atlantic with temperatures around average. The ECM however looks fine, crisp and sunny for many.

Edited December 18, 2020 by Captain Shortwave

[BLAST FROM THE PAST]

BLAST FROM THE PAST  12,241

Posted Tuesday at 22:51

Is this close enough for a B F T E?

now that’s what I’m after....love the whole run so far.  Trough to East plunging N/S then Easterly with trough to SE.....just wait for an attack now from NW/SE LP towards New Year....this must happen surely...

 BFTP

main point of this post is look at date of chart projection of GFS run last Tuesday....it’s for 27th.  Now look at this from tonights ECM for 28th

No push backs of any note here

 

BFTP

Edited December 18, 2020 by BLAST FROM THE PAST