We are coming up to the period where there was a lot of discussion re: GFS vs ECM outcomes which were very different. All the models, particularly GFS, predicted this current cold outbreak very well. In fact the most unusual thing was how much more snow there was in the East and South/South East, not forecast by anyone. It yet again proved the futility in trying to look at snow predictions more than a couple of days out whoever is saying it. So soon we will see if we get the (then) forecast GFS NW/W dominated HP across the UK next week or the ECM (then) forecast Easterly. I suspect it will be something with an easterly element, but not quite how ECM envisaged it then.

GFS 06z ens

Wah! Uppers for even Plymouth going to-10 for a couple of days on the op!

Mind you it looks a bit out on a limb also the snow row is but 3!

Looking at wind direction, there is now a significant cluster showing a quick transition to first southerlies and then SWerlies. 

The GFS ENS 850 plots are not telling the whole story and it is easy to interpret the upward swing in uppers in FI as 'mild and Atlantic-driven'.

http://www.wetterzentrale.de/pics/MT8_London_ens.png

Taking 27/1 deep into FI on the Op for example, the 850s are high, but this is due to a southerly pumping up a blocking high to the north-east. Conditions at the surface are far from mild and we see a southerly-tracking jet.

http://old.wetterzentrale.de/pics/Rtavn3481.gif

http://old.wetterzentrale.de/pics/Rtavn34817.gif

http://old.wetterzentrale.de/pics/Rtavn34815.gif

In short, high 850s do not necessarily equate to a mild outcome.  

Really?  My recollection is that ECM picked up the northerly and sustained it whilst GFS had the high flattening to the west as early as tomorrow.  As for the easterly/south-easterly flow next week, GFS didn't show that at all for several days after ECM picked it up.

Your point about precipitation is well made.  I posted in the other thread that this morning's snow wasn't correctly predicted even by the 06z, i.e. it was wrong at 3-4 hours out.  Actually the trough was far more active than even the Met Office were expecting as recently as last night, with a larger area of precipitation extending further west than expected.

Meanwhile, here's the 00z ECM ensemble for London:

Still the same trend to less cold in the 10-15 day period but less marked that in yesterday's 12z.  I commented last night that it seemed it was around uncertainties over the possible repositioning of the block or its demise.  It's only a guess but I wonder if more perturbations are showing the block moving towards the north Atlantic - as hinted at in several operational runs recently (and this morning's GFS).

Probably the kiss of death but worth remembering that, if you look at historical charts, in most sustained cold periods there are switches in pattern that must have looked at the time like an imminent breakdown. 

This means colder here then.

Potentially - at least cyclogenesis off Newfoundland is switched off. The Atlantic jetstream is also switched off. But whether that means cold for us, is as ever in the lap of the gods. It might mean a continuation of boring nothingness. It all depends on the precise location of any resulting HP cells

the ens days 11/15 are all pointing to a renewed atlantic trough (very low amoloy on the eps)  and higher heights returning to our south and southeast. if this is not going to happen then it will take the ops to head on a different track days 7/10 which the ens will then follow. as an example, the MLB next week was not picked by the ens but by the ecm op (which over did the latitude as it generally does). so we have a block next week when the extended ens originally pointed to a mean trough just to our east.  

the general rule is that the op follows the ens in that time period but I find that if ecm op is consistently going in one direction against its mean anomaly in the 7/10 day period then it should be taken notice of. at the moment the output days 7/10 seems pretty good between the op and the ens. if the esn are consistent then that souwesterly flow should come into view soon. if the ecm op continues to keep high heights close to our nw then we could be looking at extending the cold. the ens say that these heights will retrogress to a Canada and allow the atlantic to push through. interesting weekend approaching

[quote=Gandalf The White;862466]

Really?  My recollection is that ECM picked up the northerly and sustained it whilst GFS had the high flattening to the west as early as tomorrow.  As for the easterly/south-easterly flow next week, GFS didn't show that at all for several days after ECM picked it up.

Your point about precipitation is well made.  I posted in the other thread that this morning's snow wasn't correctly predicted even by the 06z, i.e. it was wrong at 3-4 hours out.  Actually the trough was far more active than even the Met Office were expecting as recently as last night, with a larger area of precipitation extending further west than expected.

I was only referring to accuracy for this current short cold snap - but it has flattened by tomorrow hasn't it. At 18z Sat on the latest run shows air coming up from Azores, SW, then West and coming across England on a NW'lie drift only from N.I./Scotland. It never showed low pressure zonality.  Unless it changes by tomorrow there is no sustained northerly. Of course your point about the Easterly is true, although that is in the future but with more agreement so hopefully will happen as per ECM :-)

What I like about both those charts is the string of lows extending from Newfoundland through Gibraltar as far as Italy. They were there on the 12z ECM op last night too, acting as a sort of foundation or barrier for high pressure to build further north.

If nickl is correct in his view that we're going to have to look to the operational runs rather than the ensembles for continued blocking, then this might be the key. It could be that this kind of string of troughs to our south is generally too weak to be picked up by low-resolution ensemble runs. (Not wishing to put words in nickl's mouth - he knows this game way better than I do.)

As I recall, GFS wanted to bring the atlantic back in by the end of the coming weekend, according to a number of operational runs last weekend and the start of this week. They also showed the HP presently to the west of thw UK sinking south towards Iberia with more unsettled weather returning to the north-west of the UK.

Good afternoon

What time do the fax charts get updated?

Thanks

It didn't - not the majority in the ensembles. I commented on them at the time. It showed exactly what it does now till Monday. A westerly ish flow around a sinking HP. It then showed total uncertainty but no defined Easterly in its operational runs as per ECM, and it has now changed and drifted towards that. This "bring the Atlantic back" seems to be a misused phrase when someone suggests the flow is from the West whereas I alway see it as inferring low pressure systems returning, which it never did.

On the basis that experience and evidence shows that the charts in the 7-10 day range often vary significantly from what transpires, how valuable are charts in the 11 to 16 day range?  I don't actually know, but I'd hazard an educated guess that in probability terms a ensemble trend at this range is 60-65% reliable?  I.e. Not really that much better than a random chart generator.  I'd be interested if anyone does have these stats. 

The key difference between ECM and GFS last weekend and early this week as I recall, was that ECM seemed to be more keen on the idea of a pressure build over the UK to some degree, followed by a rise in pressure to the east. Maybe my recollection is letting me down, but I don't remember GFS buying into the same scenario much if at all during the same period; it's solution was a fall in pressure to the NW and a westerly or south-westerly airstream becoming established early next week. OK, it didn't at any time go for a return to zonality as such, but it seemed less keen on the idea of HP being dominant over the UK and certainly didn't seem interested in any notion of an easterly.

Spot on David. The GFS evolution was a million miles away from what looks like being the outcome, whereas ECM merely committed the crime of placing the HP further north than its eventual location. Not so good for us, but still ECM had the basic synoptics nailed well before GFS did.

Talking of which GFS 12z so far:

http://www.wetterzentrale.de/de/topkarten.aspx?map=1&model=gfs&var=1&time=90&run=12&lid=OP&h=0&tr=3

Quite agree David. I'm not one for cherry picking charts, only if they look interesting from a weather point of view. ECM has been leading the way over the last two weeks or so, with GFS playing catch up, maybe as the weather is coming from a more european point of view!

There are a number who comment on a chart and say it like it "will" happen, like it is definite. Okay its what the chart is showing at the time, but all charts change, they are forecasts. I wish they could add the words suggest or equivalent. I am sure this may dumb down the antagonistic tone some posts come over as. Not up to me what they write but they want to try it and sure they would receive less negative comments themselves, unless they are baiting and what they wish for.

Back OT, and GFS flip flopping temps from its previous run at 120. Could be true, of course!

T+132.

Cold air shunted further south (so far)

To summarise - next week looks like being cold, dry and frosty for much of England. Milder in the north, especially Scotland.

Looks like our winter will not be rescued from the east ( in terms of snow, although I like dry and frosty weather), so we must look north and hope the Greenie High scenario can come off.

Possibly to midweek, after that it looks colder up here, or in the east at least before the potential ridging to/from Greenland (TBC on this evening's runs?)

T+156. The blue is really struggling - even to get into the South.

Be interesting what ECM's take is on this as GFS has not performed very well lately being all over the place playing catch up. I just would not trust it modelling this european weather, while ECM has been fairly rock solid.

T+174. Looking better as pressure rises round Iceland.