Model Output Discussion Autumn 2024

[AO-]

I will stop after this one. A big difference between operational and control at day 10. 

In the EPS a large cluster with similar temperatures, so still a lot of certainty till day 10. 

Edited November 4, 2024 by AO-

[Jacob]

The 12z GFS is definitely a downgrade. The only cold spell only brings notable cold to the north and it lasts 1 day. Fingers crossed the ensemble and the ECM goes well

[*Stormforce~beka*]

 MP-R likewise!!

[cheshire snow]

 Jacob not sure you can call it a downgrade it was a day 14 chart way out in La La land and the first bit of interest for some of the season,The ECM only goes to day 10 and would imagine it will be HP dominated.

[AO-]

 cheshire snow

Depends on the definition of"downgrade". Not a single member, as far as I can see, that goes with the Vortex over Siberia, let alone a split. The hp keeps sticking around over our heads.

[Penguin16]

What’s the chances of the cloud cover breaking up if the high centre is parked on top of us like day 7 onwards ecm

[sheikhy]

Bone dry all the way out to day 10 and beyond on ecm and gfs!!!!been cloudy here with pretty much no sun for the last 10 days!!!

[I remember Atlantic 252]

 sheikhy showers in the SE off last 2 I'd think?

[WYorksWeather]

Comparing the ECM and GFS at day 10 below.

ECM 12z has high pressure just north of the UK. Cooler with a bit of an easterly feed into the south but nothing really that spectacular. To be expected as most of Europe is still quite mild. In a colder year that might have been a more interesting setup.

GFS 12z already has the centre of the high a lot further west at day 10. Actually somewhat milder at 850hPa at day 10 than the ECM is, but the overall pattern is probably more conducive for cold with high pressure further west, and as others have noted it does go on to deliver a brief cold spell later on.

Looking at the 12z GFS ensemble (no ECM ensemble yet), it does appear that we at least have more scatter from mid-month. Some options turning colder, but overall at least initially the expectation is probably more around a return to average temperatures, rather than colder than average temperatures.

At the surface, the trend seems to be for temperatures to also drop away. Overall daily means look close to average from around mid-month, but probably milder than average by night and colder than average by day, since the pattern looks likely to involve a fair amount of cloud.

 

[WYorksWeather]

 I remember Atlantic 252 Don't see why you'd expect much if any precipitation to reach the UK at all with that. At day 10 the whole of the UK is above 1025mb - maybe an odd bit of drizzle or something but hard to imagine any more than that under this pattern.

Of course, a lot would depend on where the chart would go beyond day 10.

[northwestsnow]

 

We have energy going under that block

would be lovely if the high managed to ridge towards Greenland.

all that said the period 144-168 looks very tricky so I'll not be reading to much into the latter stages of any model as we could yet end up with a sinking block.

Last night's ec 46 not interested in any retrogression..

 

Edited November 4, 2024 by northwestsnow

[LRD]

25 minutes ago, northwestsnow said:

Last night's ec 46 not interested in any retrogression..

Nor is tonight's. Last frame of SLP anomalies (9th to 16th Dec) is pretty typical of the previous frames

Edited November 4, 2024 by LRD

[sheikhy]

 I remember Atlantic 252 potentially some very very light stuff far south east but in general just dry as anything!

[northwestsnow]

Ill be a bit dissappointed if we dont see some frosts from this.

The block sinks 

 

That's two nights on the bounce ec46 says no to a - NAO..

 

[northwestsnow]

That's said,clusters are interesting days 11+

[Mike Poole]

Notable shift in the ECM 46 zonal winds this evening, as the strong vortex returns towards average at the end of the run:

I think there might be a mix of two things going on here, both might be new developments, one good one bad from a cold perspective.

1. There are clearly some members showing a dramatic weakening, indeed 4 show a SSW.

2. The strat vortex would also be expected to slow from the really fast speeds as it becomes strongly coupled with the trop vortex, so this might be happening in some members.

Edited November 4, 2024 by Mike Poole

[Mike Poole]

 northwestsnow Yes, this morning’s GFS 6z would sit squarely in cluster 2 there, so there is some decent support for that evolution.

[northwestsnow]

 Mike Poole I'd consider it an outsider personally but stranger things have happened,I think.. 

[WYorksWeather]

 northwestsnow Yep, don't have time for a full post tonight but some of those clusters do look interesting.

At the surface, looking at Glasgow here, still no signal on the meteogram for even a drop back to average - still above average right out to day 15, only somewhat less so.

In the reverse of the more typical pattern, there's actually more of a signal for a return closer to average on the London meteogram. Note that the wind rose has a few more north-easterlies and easterlies than the Glasgow one.

 

[Cambrian]

The fundamentals of the pattern in the more reliable are very similar to yesterday’s models, if anything an improvement in terms of amplification. 

We’re still very much getting the notable dive in the jet stream over Pacific North America, from Canada south to California, now between days 4 to 7 here on the 12z GEFS mean, that sets up the more meridional pattern through North America and the Atlantic for week 2 and the scope for some cold weather down the line. From there, it’s just variation in amplitude and frequency of the subsequent waves that we’re seeing across the divergent ops, which is what we’d expect.

 

Any meaningfully cold spell before December is a bonus, like being offered a free starter with your Sunday dinner down the local. 

Here’s the improvement I’m talking about, comparing yesterday’s day 10 with today’s day 9. The core heights are modelled further northwest, over the Faeroe Islands, rather than southern Norway;

 

and the surface high, is centred over Scotland, rather than Poland. Quite impressive modifications in just a day.

 

It’s a better setup for both amplification and retrogression. The Siberian lobe is stronger and the wedge of heights through Svalbard up into the pole, and therefore the polar high, are all stronger too, serving to keep the Canadian and Siberian lobes firmly separated, and also help with further northwestward retrogression of the high pressure too.

It’s difficult to read the evolution on the means in earnest past that point, but in the meantime I’ll have the tomato bruschetta please. 

[HarvSlugger]

 northwestsnow after what it showed for last winter I do not believe it whatsoever now anyway

I remember it showing a month of blocking and cold,never happened

Edited November 4, 2024 by HarvSlugger

[virtualsphere]

 HarvSlugger As you're fairly local to me in west Wales, the 2005 setup was better for November snow than 2010 here - Nov 2010 was dry and cold, while I think NE England had some severe snowfalls out of the set up  Cambrian posted earlier.  Of course, Dec 2010 was a different story with some memorable snowfall, while Nov 2005 didn't amount to a long lasting spell.

This is a good example of the 'Pembrokeshire Dangler' setup with prolonged snow showers coming off the Irish sea giving a decent covering in our back garden:

  

In Nov 2010 the north easterlies brought the prolonged snow showers across the North sea into NE counties leaving Wales dry and cold. 

In terms of UK weather, the 6Z setup looks somewhere in between with the northerly coming down further east of the UK than 2005 spawning a low which dumps most of the snow in the midlands.

 

Of course it won't play out exactly like this and both 12Z and 18Z bring the low further west into the Atlantic giving us rain instead.  But more interesting to watch than the usual SW'lies anyway!

[northwestsnow]

 HarvSlugger

I find it very useful but like all medium range models, it has flaws.

[HarvSlugger]

 virtualsphere wow I never knew this! Thankyou 

[WYorksWeather]

 Cambrian Yep, the various pieces certainly in motion to shift the pattern beyond mid month. Of course whether it works out well for UK cold is the sort of detail we still can't see at day 10 and beyond, hence the fairly equivocal mean charts.