kold weather

Looks like a transitionary snow-rain event possibly for some on the 18z GFS as the low forces its way in and injects the WSW airflow into the UK. If only we could stop that PV lobe from exiting when it does, would probably make us lock into a solid cold spell.

Its been the low that has been ruining all the global output on the 12z suite, its more that the energy coming from Canada is strengthening the jet and deepening that upper low over the Atlantic to a point where it injects warmer air into our neck of the woods, aka 12z ECM. It does look a little flatter though this time which is good, no circle of death yet! Also, every GFS ensemble (and every 12z ECM ensemble that I looked at) all went milder at least in the south when the low took the track the 18z GFS is taking, without fail. Lets hope this can break that trend!

Low off Canada doesn't look in a great position at the moment at 126hrs...may not be the run we are looking for but still time for change!

Yeah it is actually fairly noticeable difference from the 12z run at the same point. Catacol has posted an AWESOME post in the other model thread explaining what may have gone wrong with the cold spell that the models have been trying to produce. Very interesting and feeds a tropical explanation as to why the Canadian PV has been so strong and why its kept reverting a more zonal pattern (well, NW for us, but even so...)

Could the fact that the PV is so much larger in the area it is in than normal that its distorting what would be the usual tropical forcing pattern? I'm not sure, its certainly an interesting dilemma, and as you say if we keep failing then clearly something has gone awry somewhere. No doubt if it goes wrong, it will find a way out during April or something when its of no use!

I vote Tight Isobar, he would talk rings round them all those snowmoaners!

Looks like the vortex is evolving in a positive way from looking at the N.Hemisphere charts. Need that to continue, the ICON is against some big hitters tonight, if ever it was going to pull another Feb 18, now would be the time!

Ready for another round everyone! We are certainly having to work for this one. I do with all hope, hope that the GFs 18z is the start of a shift towards the colder solutions, feel like it needs to happen soon otherwise ensembles will shift at some point.

It maybe that the Swansea grid point is actually in the water, that would explain why temps hold up on all runs a little more. We really do need some operational runs onboard from the 18z and 00z suite, or these ensembles will shift back milder again like they have done before.

Basically we want the vortex to ease to allow a cold plunge down into Europe. After that if we do get a Scandi high then as you say what happens to the Canadian vortex isn't a problem as you say. 5th-10th is still my call for decent blocking...but I think your right about the location now. Of course, the big risk is shown on the 12z GFS op, in that you do get HP building but there isn't any decent cold air pool within a 1000 miles to tap into, that run would look a whole let better with Europe being 10C colder! Matty, that is good, the closer we can have the cold pool the easier it will be to drag it down IF we can get any Scandi high afterwards.

Thanks, more support for cold BUT with a considerable minority going with the operational run. That's still finely balanced then. Great to see it in chart form, especially as it does kind of back the eyeballing of the individual runs. Also cooler further north with less milder runs, backing up the idea that the LP crosses the UK at some point o the 31-1st Feb and where it does makes a big difference temperature wise. Still, with both the GFS and eCm ops on the warm end, as well as the GEM+UKMO trending much worse...what is it the ops are seeing that the other enemsble members aren't?

Was do they look like for London? That would be a better indicator I feel in this set-up as to what the broad lay of the land is. The individual members are still something of a mess, but eyeballing it, it does look like there is more colder options than milder ones, though still considerable uncertainties with it.

Well the 12z ECM are...still all over the shop. As with the GFS, two broad camps emerge, one that sharpens the mid atlantic ridge as the PV lobe rotates NE towards W.Greenland. The other one sends it into the Atlantic a little like the OP run from the ECM+GFS. The op runs are certainly the form horse at the moment, but still options out there.

I know, we would be mad crazy unlucky for it to go wrong again, and yet the models are all lining up in a row now and I'd say its odds on now, despite what the tropical forcing suggests. I know one of the mets on an American forum says that ones of the most stubborn and potent PV lobes he has ever seen, its even too strong for them and suppressing everything too far away for them! I wonder if its just a little well entrenched and with the ENSO signal basically flatling there isn't really anything post SSW to shift the pattern that becomes established, especially as the troposphere response has thus far been pretty piddly. Just can't shif the pattern and that vortex is locked in place more or less. Also, the Arctic forecast has gone right down the pan as well recently, the upper high not making any near as much inroads.

Yeah there are probably 3 decent snow events before the whole thing goes wrong, in that regrard the shorter range is quite a decent upgrade compared to the 00z. Maybe it might be best to forget about that cold northerly that was previously forecasted and just focus on the nearer time which has got some potential, if marginal, snow events. We may miss something right in front of us whilst trying to reach for the impossible?

Yeah it may well be too mild. BUT that is run No.5 showing more or less the same evolution of the LP. Its getting hard to simply dimiss it as a bad run, especially when UKMO, GFS and GEM all evolve in broadly the same way, not exactly, but broadly. My bet is its caught onto something and got it on lock now. Hope I'm wrong though!

It was never going to disrupt because there is a weak ridge to the SE, you don't tend to get trough disruption into an upper ridge, so it held together. Anyway 240hrs has a decent mild flow in place but its not the worst ending point actually and I can see an evolution that eventually gets us into at least *surface* cold via a Scandinavian high, but it'd probably not be the deep cold variety.

I'm thinking the writing may well be on the wall again for this attempt at a long sustained deep cold spell other than maybe that NW shot, which of course could provide something decent. Will probably be another 7-10 days before the pattern may shift favourably again. GEM is all worlds of awful tonight by the way, really bad! So that's the ECM, GFS op/control + 40% ensembles, GEM op and UKMO all very much on the same page around 144hrs with how they handle that upper low over Canada. Getting to be some strong agreement there.

It did have decent support from the ensembles on the clusters though, it was pretty close to 50-50 in terms of what it did with that upper low. I fear tonight that may drop down to 20-30% but we will see, especially with the UKMO+GFS jumping onboard with it. Starting to feel like De Ja Vu isn't it everyone! Even the posters in here are like de ja vu! PS - add GEM as well to that list, BAD 12z GEM tonight, with WSW from 168hrs all the way through to about 228hrs.

12z ECM goes the way the 12z GFS does at 192hrs as the upper low is a little too strong and LP SW winds is rotated around. We do probably make the most of the set-up before that though and technically that probably does count as a cold spell before 192hrs. Cold air will never be far away from Scotland, so could easily see it being drawn back down, but probably not beyond N.England IMO. Also...note the 12z ECM and the 12z UKMO are IDENTICAL with the placement of the PV lobe off Canada, that's why I was such the UKMO would also not have a cold spell later on like some of the earlier runs did.

Yep, that's where the differences in how they are handling the PV lobe start! Much better Arctic pattern and the PV looks in a much better position and stronger on this 12z run, which may make the Atlantic low less of a problem.

Hmmm interesting 12z ECm. So the LP heads into the Atlantic, so that will probably cutoff the NW flow soon. BUT on the up side, that is decent ridging behind it and may help to give that extra push to sink SE enough to re-introduce colder air again for the south. North may keep the cold this run.

Much better orientation this run for sure on that low, uppers do look cold enough for snow as well down to low levels on this run once that cold air comes in from the NW.

12z ECM better than its 00z run, I like what its done with the low near the UK (and yes, it does look a little like the ICON).

A: Your right, but I'm 95% sure that's how it would pan out based on the fact that its almost identical to the 00z ECM and the 12z GFS with that upper low. B: Well I was right with the easterly wasn't I in calling it 'dead Jim' before most others did...sometimes it pays to overanalyse. IF you know WHERE to over-analyse! Lets hope this ECM bucks the recent trend it has had on this 144hrs chart!