Derecho

Im pretty sure Marham in Norfolk recorded a minima of -13C in the January cold spell, it got down to -11C in parts of East Yorkshire on the same night too.

Indeed, rather depressingly I think arctic ice has been affected to the point where there is no return. Yes we do usually see arctic ice extent close to near normal by Spring but the lack of thickness and multi year accumulation means that even if we do get conditions favourable for a lack of melting even for the majority of a summer it could very quickly be undone in a short period when it is not. Given the arctic is warming faster then anywhere else on the planet we really are up against it in avoiding a downward trend at the very least. Arctic ice is too sensitive even to the smallest changes that favour increased melting.

Thats for the 12Z unfortunately. The 18z is much different, the pub run hasn't really been living up to its name this winter has it?

Energy spilling between Iceland and Greenland though stops these runs from being classics. Hopefully the models are overdoing this, otherwise the really cold uppers will be redirected towards Scandi and there won't be as much impetus to drive the cold air southwards due to the high not being able to sustain itself to our NW. It would be a great shame if that was the case. There has been very cold uppers returning much later in some runs, but it would be nicer for this to be at close range, rather then looking too far out at charts with a very high amount of uncertainty.

http://www.wetterzen.../Rtavn1501.html Have to be careful the high doesn't sink due to shortwaves though, lets hope the high can maintain itself if they do happen to occur.

I've seen some ridiculous outliers at times but I think this has to be up there with the best If only, a very snowy birthday for me if that came off!

06Z looking better then the past 2 runs in terms of potential regression? http://www.wetterzen.../Rtavn1321.html Although pressure is higher over Spain on this run then UKMO and ECM.

Pub run says no to regression to Greenland though , staying sober it seems, could be one of the milder runs with high pressure dropping to our SE. Likely to be a mild outlier but a few runs were showing this, key period is the link up with our mid latitude high and the Newfoundland high between 96 - 120h. On this run the high over Newfoundland is a bit weaker and the low to W of the Azores is more troublesome. Little changes at that stage will make a big difference as alluded to earlier. But it could just be a wobble anyway.

Despite potential for smaller features to cause a wobble on this run, regression does kick back into gear http://www.wetterzen.../Rtavn1561.html Negative pressure gradient there from Gibraltar to Reykjavik, a slower regression it appears, probably won't be as good as the 12z ECM but still good to see rising heights to the NW and a -NAO.

http://www.wetterzen.../Rtavn1081.html 18z appears to show less of a link up between the High over us and the high over Newfoundland (which is a bit weaker). We shall see.... If the high is split up then this could be one of the much milder runs come mid to long range (although in the minority on the 12z ensembles) The low to the W of the Azores looks more disruptive. One run but it may show where things can go wrong( if it does, regression may just be delayed), but bear in mind there was still plenty of cold options on the 12z ens and also the ECM and UKMO runs. The sooner we see regression the Greenland the better.

12Z ensembles are a mixed bag as to the northerly later on, with some focusing blocking so far west that he end up getting warm southerlies due to high pressure to the SE, some bring in a very swift return to Spring, one or two especially mild runs in there in the low res. Still some very cold runs in there though, most notable is P4 which really is quite something. UKMO looks like it could develop into a decent northerly after T+144. The key to getting a really potent northerly is the speed as to which the high sat over us moves west, very uncertain at this point though. A meridional NH jet pattern looks likely in March with a very cold arctic, question is.... which areas are going to tap into this notable cold?

http://www.wetterzentrale.de/pics/Rtavn2161.html What a chart, strong -NAO east based (pressure gradient flow Gibraltar to Reykjavik) Low coming out of Newfoundland being disrupted heading south, while supplying WAA to Greenland. Would be nice to see this verify.

http://www.wetterzen.../Rtavn1621.html 18Z more akin to 12z ECM so far, high pressure moving further west more quickly. Will it result in blocking further east over Greenland? We shall see but good consistency on the general pattern.

Some consistent signals in the output recently with a theme of retrogression towards Greenland. Interestingly in recent runs this has become stronger. The GFS 12Z for example shows a Very strong Greenland high with higher thicknesses (High pressure covered in yellows on Wetterzentrale instead of the blues and Greens... and pressure around 1050mb still) although this run still has a rather West -NAO Whether we see a west based -NAO or East based is the big question. Given the overwhelming amount of mild Marches in the past 25 years people could be forgiven for underestimating how cold early March can be BUT we have some of the coldest uppers I have seen for the past 5 years at least in the arctic. Now would be a good time to tap into a northerly. Providing that regression takes place even a west based -NAO( Although not too much), it would still provide something wintry, however if we get an east based negative NAO we could well see a very notable cold spell for the time of year. However a long way to go yet before that is decided. Good trends though.

A very good ECM run with the NAO finally going significantly negative later on in the run, hope this becomes a growing theme over the next few runs, I can imagine a few frames later the ECM would be getting really interesting

More notable is the change of alignment of the direction of the cold uppers too, heading in a westerly direction rather then south westerly, I'd be surprised if this was the start of the trend given the past few runs but fingers crossed for you guys in the SE, small margins could mean notable upgrades if you get lucky.

Agreed, the more energy we have to the SW the more the block will be supported and also more cold we get under the block heading west the better. The 12Z is a slight improvement, with -10C uppers making a more widespread appearance in the far SE and also the high ever so slightly further north. Looking further ahead the low around Newfoundland at T+96 gets stalled around Greenland forregression of heights NW and a negative NAO, but this is a while off so can still change.

Good Morning All Output this morning hasn't seen the high move north. unfortunately, but considering the spell of wet weather we saw around Christmas it could be worse. Cold and Sunny would be my take away from the SE and the channel Islands, but as I say it could be a lot worse and indeed very winter like. Cloud cover remains uncertain and with the windchill it will definitely feel a lot colder, with temperatures dipping below freezing for many, temps generically around 2 - 3C below average. What happens to the high is anybodys guess at the moment, but the jet profile over the USA from day 6 - 14 generally doesn't favour a particularly positive NAO. GFS once again attempts to dislodge the PV over NW Russia but sinks the HP after making an attempt to move NW somewhat, but FI usually likes to be overly progressive anyway.

Daytime temps will be around 3-4C around the CET area as a rough guide and -2 to -6 quite widespread but dry for a lot of the uk with only the SE getting some snow on this run. Uppers may well be below -10C in the SE at times but high pressure could cap the convective potential a fair bit. For the SE/ Far South/ Channel Islands the excitement is understandable. However for most of the UK it looks rather cold and clear. It would have generated more excitement a few years back but this was because we went through an unprecedented high amount of warmer then average winter months coinciding with a lack of snowfall from 1988 - 2008.

Rather Bland run for the GFS 18z at close range with even more of a southwards correction! http://www.wetterzen.../Rtavn1441.html There has been a theme for heights to the NW but still a loong way off. At this rate only the channel islands will receive snow. Ians thoughts earlier seem to be showing in the output now, the incapability of a strongly negative NAO showing its hand once again. The output next week looks rather boring for the vast majority of the UK. Only one run but it's beginning to resembles the first half of last December a lot! Roll on Spring.... the lack of serious heights to our NW has stopped this winter being a classic. Despite having a lot of ingredients for a very cold winter in place beforehand we havn't really managed to get anything special, rather something very normal. (slightly colder infact but consistently near normal) March can still surprise but the likelihood of really notable cold spells starts diminishing now. Maybe a Greenland high could develop but we shall see... Hopefully something that will feature more next winter. It can still change but the closer we get the less likely we will see a correction in our favour given the trends today.

Pretty bland runs for quite a lot of the UK, dry and cold is what will probably verify, if that low ENE of Norway was more shallow the high could budge further North, energy starting to go North so the high under pressure to sustain itself at a northerly latitude. The NAO is now struggling to go significantly negative, the major achilles heel of this winter. Would make for a bland cold spell here. EDIT: Although the later part of the high res sees a better attempt at getting the NAO to go negative.

The low to the ENE of Finland is a fair bit deeper on this run and hence has the block a bit further south, which would increase the stability a bit further here in the NE, not looking as good, more in line with 00Z UKMO and ECM. The UKMO is even slower.

Not yet, summer comes in April or May if the past few years are anything to go by. On a serious note, just because we are a third of the way through February doesn't mean we can't get anymore potent cold spells. The first 20 days of March 2006 for example were great here.

18Z run looks rather benign with the Azores high Starting to link up with the Scandi high however the second low may undercut.... hopefully we may see the trend for a Greenland high again later in the run because it has disappeared recently. The 18z reduces the influx of cold uppers in the short term yet again. The achilles heel of this winter is the refusal of the NAO to go negative. If the Azores high was weaker I think this would have been a classic. I think we have managed to do very well this winter considering the poor synoptics we have seen. Still we may get a decent covering early next week, very borderline though. After that I hope the high over Scandi can strengthen and lead to some decent blocking but that is a long way off yet.

I wonder if we can beat February 2010's figure of 2.8C to make it the coldest February since 1996?. A very fair chance of this happening IMO, maybe 1991 even. The signal for a Greenland high building later in the month is very strong. We are also long overdue a cold March (2006 and 2001 were cold but not especially so) again 1996 was the last one, might 2013 be the year? The dominance of very mild February's/ March's will IMO cause a lot of people to underestimate how cold late Feb/early March can be if this does turn out to be the case.