The GEFS disappointing. you really need to see more agreement. A poor ECM could cause some wobbles in here later

Getting to a cold spell is never easy!

 

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http://old.wetterzentrale.de/pics/Rtavn721.gif

http://old.wetterzentrale.de/pics/Rtavn722.gif

Nice! Definitely snow potential for Eastern Scotland and NE England. Think Fife/Tayside, maybe down towards the Lothians too. 

All in the reliable now as well. :-) 

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Not IMBY. 12z GEFS are showing far more agreement on the colder runs in the mid term (5 days) than the 6z

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Some good model runs this afternoon if it's cold & possible snow you're after.

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A skeg shows there are still perturbations that collapse the block but you'll very rarely get GEFS agreement at D5.

Go for at least cross-model OP run agreement at D5 and you're almost there. ECM is, well you know, the 'c' word this evening. Get the D5 to match and the de-icer can be put on standby.

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That c word could cover a lot dependent on the charts 

That's a bit misleading , looked through all up to 180 and most keep something from the East

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It's 'crucial' by the way 😉

 

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Short term ens

The Aberdeen equivalent looks rather chilly http://modeles7.meteociel.fr/modeles/gens/graphe_ens3.php?x=&ext=1&y=&run=12&lat=57.2&lon=-2.3&runpara=0 

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Possibly there are quite a few ingredients to get a good lake effect

1) High vertical temp gradient (>13C to 850hpa): Check, 15-19C typical values

2) Cold air advection: Mostly check, although later on in the period there is warm air advection.

3) Moderate speed sheer: Speed sheer seems quite low, could limit convection as updrafts and downdrafts interfere

4) Low direction sheer: Directional sheer is very high. This seems like a convection killer to me

5) Long fetch length: Check

6) Reasonable moisture content: Check at first (despite high pressure) but air dries out a lot later.

 

Honestly it doesn't look good, the vertical gradient is good so there should be some decent CAPE and low level instability but high directional sheer and low speed sheer should kill off any showers as they form.

 

 

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Well, here would be my observations for the evolution from this afternoons suite

* Forecast blend - Aperge / GEM blend

* Runs dismissed - GFS / UKMO

- reasons

Aperge & GEM are bringing lower heights to the east of the UK & not lifting them out with a SE flow - keeping low pressure well to the SW- this looks spot on to me. Cold pool circa -10 lingering for longer than projected in other suites a la GEM.

GFS dismissed- to much deepening of atlantic trough @ 120 allowing increased surface SE flow across england in the mid term lifting the cold out- the angle of SE will I think be wrong, future runs expected to sharpen up the trough leaving a more Easterly flow over the UK

UKMO only dismissed due to heights being to high to our east & perhaps to much of an ESE flow - but a lot closer to Aperge/GEM blend than GFS

I dont usually follow the GEM however by luck or judgement I think its spot on this time with the emphasis on a stalled out cold pool 'somewhere over the UK or close over holland' hols a lot of credibilty due to the heights building in situ over the top between 144 -180

Lets hope ECM poor form over the last 5 days is rectified this eve....

S

Interesting stuff. Cheers Q. 

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Meanwhile, at closer range a cyclogenesis event will take place over the North Atlantic in the next 48 hours, but mercifully on this occasion it is true that worse things do happen at sea . . .

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GEFS  12h splits cold:mild

120h 90:10

144h 70:30

180h 70:30

240h 60:40

360h 45:55

Ens looking a bit more variable Could however give more opportinuty for precipitation rather than just cold dry.

 

 

 

Evening GEFS has trended colder mid month. The angle now will be the first nationwide cold spell since 2013. Snow obviously to be decided.

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http://old.wetterzentrale.de/pics/Recm721.gif 

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Grey cold and damp with bitter wind. Can't wait.

Well you're going to have to, so be patient 

More of the same down the line and then it goes similiar to the 00z op run http://www.meteociel.fr/modeles/ecmwf/runs/2017020512/ECM1-144.GIF?05-0 

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Not so good at 144 on the ECM but bordering FI range by that stage!
http://www.meteociel.fr/modeles/ecmwf/runs/2017020512/ECM0-144.GIF?05-0 

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Some days you just wish you could smash up the ECM.

Poor form for 5 days - now a 6th day, the model every day has corrected the 120 > 96 & the 96 > 72 to the UKMO..

Ecm utter crap by day 7 let's hope its completely wrong. Big day tomorrow 

http://old.wetterzentrale.de/pics/Recm1681.html

 

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Oh well, at least it's not consistent and the ensemble data may, once again, be better.

The ECM op run is very much on its own at that range. Here's the JMA for comparison http://www.meteociel.fr/modeles/jma/runs/2017020512/J168-21.GIF?05-12 

It is either doing much better than all the other data and has picked up a new trend or it's wrong. Time will tell but I would be rather surprised if it wasn't on the milder side of its ensemble suite later.

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How do you do the math can I ask?

Ensemble No 14 is by far the coldest from +192z - Just wanted to display these - I have chosen the chart for the same time on each day.

I just love how it goes from south south-easterly at +192 to Easterly then north to north -easterly.

If this materialised it would be the coldest spell since the winter of 2012/2013.

Also notice no Azores HP!?

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That's quite a pressure gradient, 113mb range on that chart!

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