Ian Brown

Phil, there were ensemble members on earlier GFS runs that must have shown what we have now seen from the GFS OP - it so nearly happened on the 18z. If the Highs do not link then it is a potential game changer - southerly tracking Lows, PFJ straddling the UK etc... is only any good if the core centre of the High is to the North or North East - not over Greenland.

I don't trust the accuracy of the UKMO at T144. I never have and find that it tends to follow the previous ECM run. For those saying that the GFS still shows fantastic blocking, yes it does but we would most likely be on the wrong side of the PFJ due to the likely orientation of the High. We must have the link of Highs to be on the safe side.

This GFS run shows what the 18z so nearly showed last night. We must have the link up of Highs and on this run the shortwave spoils it. Nervous times ahead. Ensembles waited for.

The GFS operational was at the cold end of the ensembles for next weekend, and there still seem to be plenty of options on the table.

What we don't want to see is the European trough any further S/E than it is on the GFS - whilst on the ECM we don't want to see it any further N/W ! The METO removes it's shortwave that it had on last nights 12z. The link between the Arctic High and the Atlantic High is coming closer and the models are firming up on it. No guarantees yet though. Omega block by the end of the ECM.

T192 and a monstrous block is in place, very difficult for the models to handle this sort of situation going forward and probably more changes before that in earlier timeframes. I would think the easterly/north easterly flow would now be progressively colder so the dam and upper air figures on the charts are probably not the best guide the longer it goes on.

T174 and the Atlantic is beaten with the heights dropping towards the Azores as the block asserts from the North. Should be subsequent frames showing the colder air reaching these shores but if the 18Z does verify in the T108-T156 sort of range (and that's a big IF) then there is absolutely no margin for error in those developments.

T156 and where are we going ? The warm front sits a few hundred miles West of Ireland but are heights rising enough to the North to scupper the Atlantic ?

Its only the 18z but the link up between the Atlantic High and the emerging Arctic High is looking very tenuous at T144 as low pressure is further NE and this is the threatening the block. We must have that link up IMO.

Different solutions this morning with the GFS delaying the cold uppers and then phasing occurs with a Low to the SW, potentially spreading milder air into the Southern areas at least until colder air returns from the North. The ECM ends up essentially similar to last night's run but there are uncertainties in the medium term. We must see the High to the West link up with the High pressure coming out of the Arctic if this is to be a long lasting cold spell. I'm not a great fan of the accuracy of the UKMO T144 but I'm not sure we would see that if they went out to T168 but its open to conjecture.

The differences on those ensemble scatter surely reflect the Low positioning, many places here would be colder than De Bilt if the low is sitting over Holland.

Steve, do you really think that flow would be extending much beyond T240 ? I think the High would end up on top of us by day 11/12 if the run were to verify.

The ECM changes from it's morning position of retrogression to Greenland to maintaining the NErley at T240. I think it would sink thereafter with pressure lowering over Greenland and the Atlantic High looking leaned on. However, pretty rarefied synoptics before then and T264 might as well be T2000. Bound to be plenty more changes over the coming days.

Yes of course T240 is a long time away anyway, and I think we had a lot of concerns about this Western based NAO prior to the mid-December 2010 outbreak, which proved to be unfounded.

Very interesting output this morning, the GFS goes for a link up with the High to our West with emerging pressure rise over Scandi prolonging North Easterlies over the UK, whereas the ECM goes for retrogression to Greenland and lowering of heights over Scandi.

The teapot is not the issue Steve because in those days, these projected synoptics would be unthinkable anyway. The imponderable is getting the cold uppers here and maintaining the block, we need the upstream pattern to remain favourable, it's difficult for a block to hold around Svalbard unless you get an excess of energy going into the Southern arm.

Just a quickie as stille at work - basically the models are not going to have a clue about handling HP in the Svalbard area, so it's best to concentrate on this side of T192 rather than get excited or depressed about what the GFS shows beyond it.

As others have said, we shouldn’t get too hung up on the what the ECM 32 dayer is showing in it’s latter stages – it would be astonishing if Northern blocking could sustain for weeks on end – if you look back at the classic cold winters, you have oscillating blocking patterns and for a location like ours to keep the Atlantic at bay for such a long period would be pretty rare. Coming back to what is at hand, the trigger for the pressure build to the NW initially is now very likely and a clear evolution. Whether any of this results in cold uppers extending to our shores is another matter.

Agreed, whatever the possible marginality inland it would be no good for coastal areas. Nice to look at these synoptics nonetheless and I think some sort of major pattern change is guaranteed. However I would prefer to see a true cold feed shown (sub 528 dam and sub -7 uppers) and the only way to get that at this stage is a through North Easterlies or Northerlies and both appear to be off the table at least in the first phase of the blocking change.

The source of the air suggests not - I would think even if you got some snowfall mixed in, less cold air is behind (like Feb 10) to bring about a quick thaw.

Indeed. Prior to 2008, the charts could show all manor of things even at something like T192/216 and you could bet your bottom dollar that a spanner would be thrown in the works, usually in the form a shortwave, to pull the jet further North.

Indeed Steve, but it will take longer than 8 days to get any proper cold air here. Some potential great blocking available but we will need the pressure alignment to be spot on to tap into the eventual cold air from the N/NE/E. SEerlies are not going to be much fun at this stage.

Where the GFS is trying to initially build the heights is a difficult struggle for the models and you never see that sort of development pinned down until it is within T144, probably within T120. But if we are looking for cold I would prefer to see the sort of evolution shown by the 06z or a northerly, as a E/SE feed off the continent is not going to much use in early season and with the continent above average.

I'm not a great fan of the 06z whatever it may show. The ECM is flat this morning, but there is still no consistency in the NWP, often when we are heading towards a pattern change, 'FI' continually shows one scenario on and off for several days, but with this there is no consistency and you can see why the METO are being non committal in their medium to longer range daily outlooks. As Nick says though, timing is important and if you don't get the change in synoptics when there are possibilities there, you can find the default pattern is suddenly back with you.

The ECM at T216/t240 is hugely different to what it showed last night. The overall trend remains positive for cold fans but with such diversion in where any blocking is, hard to be confident about any solution beyond next weekend.