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Model output discussion - Post SSW - Will it turn cold?


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The much talked about SSW has taken place, but as Nick blogged about a few days ago, it doesn't always mean cold for the UK. The signs are good though (if you like cold that is), and the model output is showing a lot of northern blocking currently. It's set to be a really interesting time to follow the models if nothing else, so please carry on the discussion here. 

As ever, please keep it to model discussion only in this thread.....

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4 minutes ago, Man With Beard said:

And so we get into "squeeky-bum" time with the SSW and its impacts on the models.

Anyone looking for consistency in the fine details will be disappointed if they compare yesterday's UKMO T144 with today's T120:

UW120-21.GIF?13-17  UW144-21.GIF?12-12

Not a good start this evening with the GFs following in the same vein ?

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4 minutes ago, Man With Beard said:

And so we get into "squeeky-bum" time with the SSW and its impacts on the models.

Anyone looking for consistency in the fine details will be disappointed if they compare yesterday's UKMO T144 with today's T120:

UW120-21.GIF?13-17  UW144-21.GIF?12-12

gfs-0-120.png?12

GFS agrees 

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1 minute ago, frosty ground said:

Before we get toys thrown about the GFS is not to different from the 06z

gfs-0-126.png?12 12z vs 06z gfs-0-132.png?6

Heights are 200miles further south. It's not a great start. It's delays well see if all routes lead to cold soon

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npsh500.pngnpsh500.png

hgt300.pnghgt300.png

Arctic ridge better toward the pole than the 06z and jet cutting south a little further west. Small tweaks so far.

h500slp.pngh500slp.png

Today has so far seen the old solution of the Azores High building a ridge to Scandinavia put aside in favour of it being overrun by a low that then cuts down through Norway - thanks to that curve of the jet down south - and so acts as a 'trigger low' for the easterly as heights rise across Scandinavia from the north. This 12z run from GFS seems to be trying for yet another way forward though, as the low doesn't separate from the main Atlantic trough and we're looking to rely instead on the increasing heights down from the Arctic plus above in the stratosphere to disrupt the main trough.

 h500slp.png

A hint of that going on as of +135 (tiny low in the N Sea). 

Not as fun as the 06z but UKMO is keen to give this idea the thumbs-down with the low separating very cleanly indeed;

UW144-21.GIF?13-17

It's handled the Atlantic trough pretty strangely but that push of heights from the SW should interact with the forcing from the SSW to build a Scandi high by Tue/Wed.

Clearly, some details sorely in need of resolving before we can start expecting the easterly to land on any particular day.

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I’m not sure what the GFS is doing here, it looks like the blocking high could be flattened which is a bit of a shocker!!

edit - wrong , looks like a WAA reload will fix that

Edited by Ali1977
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Phase 1 is a fail I'm afraid on both UKMO and GFS with the ridge being overrun.

gfsnh-0-156.png?12

That means for any cold we would have to wait for the Atlantic to reamplify.

While that may be the case it is obviously much better to get the initial ridge because the next chance is again in FI and that could go wrong too.

Nothing to say the models won't switch back to the more amplified pattern they showed this morning so no need to panic yet but also no point pretending the output is not worse than this morning for cold lovers.

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2 minutes ago, Ali1977 said:

I’m not sure what the GFS is doing here, it looks like the blocking high could be flattened which is a bit of a shocker!!

edit - wrong , looks like a WAA reload will fix that

gfs-0-156.png?12gfs-0-168.png?12

Exactly the high is building again.

No quick route to cold, but no flattening high either.

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3 minutes ago, Johnp said:

I'd call that quite a big difference.

Perhaps but looking at it broadly it’s not hugely different minor adjustments equate to big impacts on resultant surface conditions. The AO definitely seems more negative on this run...

0A541CB3-B292-429E-90F8-2827B4D44DE7.thumb.png.a49786ca8d1f0fd4c73b05525b34449d.png

Edited by Daniel*
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The cold air is obviously restricted further east on this run, then again it may just be a mild outlier or a rogue run. Lets see where it goes from here.

gfsnh-1-180.png

gfsnh-1-186.png

Edited by Paul
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npsh500.png npsh500.png

While it's still making progress toward a similar outcome (trough breaking down, some of it likely headed for W. Asia with blocking to N of it), this run is a bit out of kilter with the other models terms of how much the Atlantic trough advances NE days 4-6, so is worth viewing with high(er than usual) suspicion.

It's pretty much a reversion to the 00z run, which was followed by the quicker 06z run (in terms of cold air arrival from east).

 

UN144-21.GIF?13-17

Here's UKMO top-down at day 6. Looks alright when taking into account the fact that the focus of heights is ready to shift from SW to NE of the UK - but true to say, it could easily have been better with the shape of the Atlantic trough.

Edited by Singularity
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2 minutes ago, Singularity said:

npsh500.png npsh500.png

While it's still making progress toward a similar outcome (trough breaking down, some of it likely headed for W. Asia with blocking to N of it), this run is a bit out of kilter with the other models terms of how much the Atlantic trough advances NE days 4-6, so is worth viewing with high(er than usual) suspicion.

 

UN144-21.GIF?13-17

Here's UKMO top-down at day 6. Looks alright when taking into account the fact that the focus of heights is ready to shift from SW to NE of the UK - but true to say, it could easily have been better with the shape of the Atlantic trough.

Worth Noting the Low has slipped south on the UKM whilst on the GFS it went back north west.

Edited by frosty ground
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