Granted though the amplification is much larger on the 6Z; and is less zonal.

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For all the talk of downgrades, the current charts offer far more chance of snow for wider areas than the more straightforward northerly blasts we had been seeing.

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Well I'll certainly take T+168 onwards.

Gonna be a tad windy

 

Quite possible you will see actual real blizzard possibly whiteout conditions to very low levels.

 

 

 

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To be honest I doubt there would be much snow in a pattern like this. Warm air gets secluded to the centre of occluded LP systems, the real cold air is out west. This kind of situation would be good for Northern Ireland (and possibly Ireland in general) aswell as Northern and Western Scotland but not for anywhere else. Also a strong wind means you don't benefit from any evaporational cooling so you need really cold uppers to get snow; probably lower than -8C.

 

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No it isn't, even a meridonal flow will have turns within it, which by definition will flow west to east. So basically you are saying that unless the earth rotates the other way, the flow is zonal. And a meridonal flow is basically cross polar.

Zonal is a flat jet across the atlantic, with fast flowing low pressure systems.

6z looking good, but one run.

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Looks like we could see a thunder snow event next Friday!? North sea trough could bring down more intense rain and snow or rain turning to snow!

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At +168 - quite a block right over pole.

 

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No I never said it has to run exactly along latitude lines, that would be ridiculous and make every pattern meridonal. But at the very least the general pattern should be crossing more latitude lines than it is crossing longitude lines. While that may be the case for the 6Z it was not the case for the 0Z which was not amplified enough to be considered meridonal.

This is more of a zonal pattern because the upstream jet stream is mostly moving across constant lines of latitude.

 

This is more of a meridonal pattern because the upstream jet is mostly moving along lines of constant longitude.

 

Ultimately this is subjective to some degree, but the previous poster was not wrong to claim the overall pattern was mostly zonal. I've clarified in edit that I'm talking about the upstream pattern. The downstream pattern is meridonal in both, but we don't really care so much about that.

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I think, looking at these, that although there is a lot of uncertainty you'd have to conclude that it's more likely to be cold than mild after the 8th of December :-)

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I'm still very much an avid supporter of the '552 acid test'. This is usually an excellent threshold for the UK ending up with extended cold. if the 552dm line gets to greenland I'd say there is a greater than 50% chance the UK will eventually see mostly northerly or easterly winds. Conversly, if the 552 line fails to get to greenland its more likely to be a toppler. Below is the 6Z compared to the 0Z. The 552 line is much further north and over southern greenland. The further north it manages to get the better.

 

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Then after +240 it looks like a cool N westerly from a north west south east jet with perhaps northerly one day of less cold weather. But generally cooler weather more showery. Instead of the usual SW to NE jet bringing in mild weather with wind and rain only. The air is coming from Greenland instead of the Azores - that being said it's a shame we build that weak ridge in the Azores which doesn't help things! - A long way off now but things are looking more positive for wintry weather as we head into Mid December. Impressive about the blocking over the pole. - Looks like an extensive NEGATIVE AO.

 

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Some definitive signs of a blocked pattern to the North/East on the 6z...Could this be a sign of the heights moving southward from out of the arctic...Its only one run but a continued variation on a theme....mmmm ..

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I think the models are having trouble with the fact the PV just has not organised this year. It also happened last year and the models were chucking out silly scenarios as well. (Yes I know what last winter was like - dry as a bone down here - and certainly not classic zonal).
That is 2 years in a row that we have had a disturbed PV at the start of the season.

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Lets just hope it doesnt get it act together as quickly as last year.  It just reappeared magically in the space of a couple of runs just before Xmas.

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You were beaten to that one decades ago. Will Hand posted this on usw in 1998 - and note that even then, Miles extension was regarded as an ancient rule!

A warm USA and in particular Canada is *one* of my criteria for a cold winter.
Yes it is all to do with the buckling of the jet stream and what we call Rossby
waves around the hemisphere. A stationary pattern with a warm ridge over Canada
would normally give a cold trough close to UK. A rule that works particularly
well is Miles extension which says that if one gets warm air advected north to
the west of Greenland then downwind (further east) a cold plunge will take place
55 degrees longitude east of the warm advection. This is a very old rule,
(probably no longer taught, I did) but it does work. So look out for warm
advection (usually >540 DM) west of Greenland. No doubt some old lags can
amplify a bit on this !

 

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MOGREPS and ECM ens supportive of a strong northerly orientated flow by Thursday next week - many the idea of a very deep low pushing a strong cold front across the UK. A Much better blocked pattern than what was on offer yesterday.

 

So, are they suggesting the pattern will persist for longer, as it still looks like a 2 day wonder with the cold air mainly to the North?

 

 

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Models are not without interested again today I see.

As long as the jet remains in a amplified mood, than the risk of some potent northerly outbreaks continues.

ECM 00z actually has a snow to rain event between 216 and 240s for eastern areas of the UK.

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We should set up a physical manifestation of the Winter Optimism Index and wire it to a generator.

Given the wildly fluctuating emotions displayed by some over the past couple of weeks, the oscillations would likely power a small town.

 

Heartened to see the swing back to cold after milder solutions were to the fore yesterday - but concerned we'll flip back again at some point over the next couple days.

It does demonstrate more than usual how small differences can lead to huge impacts downstream.

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Just had a look at all the ECMWF ensembles. They are alot better than the OP implies. The majority are northerlies at day 10 (albeit often imperfect ones). Very few have a dominant Azores high as was indicated on the EPS last time I looked at them all.

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Well I can only speak for the ECM when you run it further out but they obviously begin to differ in outlook. There's plenty of blocked cold options as I can see together with v active looking cold zonality, certainly doesn't look mild to me with a quite a southerly jet stream in many.

GFS   06h has a snow event from 162 to 192h

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=162&mode=2

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=192&mode=2

However

1.I doubt the LP will finish up in the position  shown-much more likely to finish up further east giving glancing  northerly/north westerly.

2.Even if the LP and uppers were to confirm it looks very marginal between snow and rain for much of the country

 

Interesting


https://twitter.com/fergieweather/status/936557570843709440 

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