kold weather

Very close run thing on 120hrs ECM. The 144hrs will be very telling, remember watch what the low thickness does over Canada. A generally north motion of any kind will be good for a cold shot at the end of Jan. Any south, and it increasingly kills that cold shot dead for most.

Chris, it would come around 168-192hrs as that large area of lower thickness/pressure forces the jet into the westerly pattern it has on the 12z GFS, you'd keep a cool WNW probably till then, but the LP would come into the Atlantic and eventually turn winds WSW/SW, once again like GFS. I've made a post which has been quoted in the other thread explaining how that would work in practice. 96hrs and the ECM handling of the upper vortex over the US and swinging into Canada looks better for us...but hard to know without seeing the 96-120hrs progress whether its going to make any difference.

It is running at a higher resolution but at the moment it has shown no real progress against the old GFS in terms of verification stats worldwide. ECM still in the lead on that front, though abit more even in the last month than previously, where ECM was heads above the others in verification.

Right well the 12z ECM is off. Remember folks, if the upper vortex over Canada dives SE towards Atlantic between 120-144hrs its not looking good, if it rotates around the upper low we will be in business in all likelihood. Beyond that and there are still going to be chances, so don't get too downhearted IF the ECM does indeed continue on its merry way. Does NOT mean its the end of winter, or that we won't get any cold for the rest of the winter, etc...maybe just make it a little harder, that's all!

Yeah, there is definitely a signal for a Scandi high deeper into the run. Though they are right, most of the easterly's are of the useless grain producing variety, with very little in the way of meaningful deep cold at all. Still need to be in it to win it. Regardless of what happens to our next set-up, still needs to be watched...though to go again for a 3rd time will be hard for people if that is what happens...

Definitely noticed that, mind you a lot of those are the poor variation of an easterly with little to no deep cold due to the evolution of the previous 10 days. Regardless of everything else, I still think we will get some good blocking at some point, I'm still happy with the 5-10th Feb, but I think your right in that area to watch may well be Scandinavia. Just hope there is a decent cold pool around by that point otherwise might be one of those HLB that looks impressive but little to back it up at the surface!

Just to give a quick illustration of the two broad camps: Here is the GFS OP and Ensemble no.7 one fails at the northerly, the other comes off. So here are both at 108hrs, I've circled the area to watch: Both PV lobes are in a more or less similar location and strength. Differences start to show at 132hrs: The P7 run keeps it as one discrete lobe and moves its around the stronger vortex lobe to its NW, in a fujiwara method (spinning around a central point). GFS Op on the otherhand is literally slicing away the energy and it is escaping into the Atlantic, just like I highlighted on the UKMO 12z as well. And VERY different 156hrs charts. The Op has a flatter pattern and the NW flattening to a westerly, the P6 has a much more amplified pattern and a northerly. So in future, if you want to have a good clue as to what way the runs are going to go, LOOK at the lobe over Canada an d its movement. IF it looks like P7 its game on, if not then there is trouble. EVERY single run that looked like the OP on the ensembles went on the flatten the flow and introduced milder air to the south. Every run that looked broadly like P7, was either cold, or very cold. We should have good clue about the ECM between the 960-120hrs charts, and almost certainly know by 144hrs.

It actually sticks out abit of a synoptic outlier, in that it doesn't send the energy across the Atlantic but equally it doesn't keep it far enough west to prevent the Azores high toppling down. Interesting run though for sure, and certainly different! ICON still just about ok as well on its 12z run.

Ok so the ensembles are once again a big mess... However we clearly have TWO clusters at play: 1: Follows the GFS op + UKMO and takes the Polar vortex lobe over Canada into the Atlantic, it merges with a low further east and the whole thing collapses. 2: 06z GFS op run - basically the PV lobe rotates around the main lobe and doesn't come away and remains over Canada/ far W.Greenland, thids allows pressure to rise and we get our northerly. Much more binary set of runs than we have previously seen. Probably still just about more support for cold, but like the ECM its basically close to 50-50.

Much better placement of the upper low over Canada on the 12z GFS para, this should be a better run, especially for the southern half ad they will get the cold this time! We should know by 120hrs by the way whether the ECM will be good or not tonight, all depends on what it does with that upper low.

Hi mate, the Azores high looks t4he same to me, remember to ignore the surface features and concentrate where the lower/higher thicknesses are. That will give you of a clue of where things are. In this case both models have the Azores high ridging about the same amount. Where is the highest thickness both runs...yep, just east of the Azores. Maybe a visual will help show the of the drivers, and why the runs are actually synoptically VERY similar. 1: Is the PV lobe that is heading SE. This force the jet onto a flatter trajectory which in turn flattens out any ridging. We saw the consequences of that in the GFS run. It is IMO by far the biggest part of this puzzle. ECM is nearly the same as well on its 00z run. 2: Is interesting, that is a weak high pressure cell, probably given the space to breathe due to No.3 being differently modelled. But the GFS is evolving it in the same way, just a little less robustly. BUT that sort of high is not the sort of high to stop the PV lobe (no.1) from coming south-eastwards 3: Is the main LP that is meant to come SE towards out shores. This is the feature isn't quite as well formed on the UKMO so the uppers aren't quite as cold. I hope that helps explain why I think they are similar? It is just my opinon and I suppose you could again call it over-analyse, but there ya go! Surface pressure do not make a pattern, but the 500mbs reflection usually will as that reflects the upper levels better (aka the lower part of the jet would be close to here).

UKMO and GFS ARE similar in where they are putting the broad pieces. Of course there difference in surface pressure but *look* at the UIMO progress from 120-144hrs and notice over the states where that PV .lobe is going....its going SE into the Atlantic. Take a look at the GFS 120-144hrs over the states (nOT the low pressure, follow the purple low thickness) where is it going, SE into the Atlantic. That is the feature to watch as it is a direct lobe of the PV splitting off, and that is why I'm confident the UKMO follows the GFS+00z ECM at least until 240hrs because that track of the upper low into the Atlantic, quite clearly lots of energy about to head into the Atlantic based on that 144hrs UKMO, perhaps even more than the GFS.

Well that wasn't the best GFS run I've ever seen, still got a few chances but we basically end up with a good, but short lived NW airflow and a really weak NE/ENE airflow and that is about it for the cold spell for most... Not exactly what we are looking for is it?! GFS 12z gets a 6/10 from me. Not a total disaster as some are saying, but its a pretty poor end given the potential that is out there.

Totally agree, and we need to see where it fits on the 12z suite of models...BUT so far the 12z UKMO totally back its synoptically, its got decent support from the 00z ECM ensembles and obviously the 00z ECM. That's actually quite a solid grouping supporting that evolution. The same exact thing happened to our last easterly attempt.

Out to 300hrs and indeed a useless easterly has arrived, probably very dull and cloudy with grains of snow. Nice warm surge coming into southern Europe as well by the way!

The thing I'd say to that is the op ECM backs it (and has done now for 4 runs), as did nearly 50% of its ensembles...as does the UKMO 12z to an extent. Itsd certainly looking increasingly probable that this is the evolution it takes. Indeed if that is the way it goes I would not rule out an easterly still at some point...but based on the lack of cold air around, probably one of those useless types!

GFS 12z doesn't look that bad synoptically. Just shove that low a 100-200 miles south and you've actually got a very good run again. Indeed may still evolve into something 'ok'.

Its not the worst for sure, but it probably makes it very unlikely the south is going to have enough cold advected down to make a go of it, especially as the synoptics don't look that bad to me still. May still be a good run for Scotland/N.England as they are just that bit closer so have more leeway. For the south, probably game over on that run, at least for this attempt...there may be others. In a westerly flow you really need -6/7C even for it to be marginal unless you have some really impressive upper cold with it, due to the Atlantic warming the lower level of the air in transit.

A lot would depend on how convective it was...but my best guess is wintry is the best way to describe it on the 144hrs, due to factors I've previously mentioned (warmer boundary level due to higher SSTs on a west track, 850hpa temps looking marginal, etc). Yesterday was good for some places BUT that required a very active trough, good timing (aka coming at night) and the prolonged nature of the precipitation dragged the snow line down enough. For example I'm about 20 miles south of Reading and got diddly because it came just a little bit earlier and the rain wasn't heavy enough, hence just rain with a touch of sleet at the end.

Its not quite as bad as you think, still some possibility down the line. However it is a big set back that is for sure, and the pattern upstream doesn't look amplified to any major degree so any cold still probably 3-5 days away from 180hrs on this GFS run. Still, I did warn people to take heed of that 00z ECM this morning, its usually been a trend setter this winter...and you always need to pay attention when it locks onto the same thing for 3-4 runs soild whilst all other models are flipping around.

About -6/7C I'd say, worth noting if you didn't get the heavy convection, there was no snow, so I for example had just rain and backedge sleety stuff due to the precip not being intense enough. The heavy showers (and they were impressive) helped drag that snow level down, as did the persistence of it. UKMO has slightly higher values...BUT the air source is from the west so the boundary level is going to be moderated by even milder SSTs than yesterday on its way here, probably what makes it the wrong side of marginal for me unless you have altitude.

Well 12z GFS is a near identical match for the 00z ECM apart from a slightly stronger LP. That's what you call a match! No real upstream ridging so on this run out to 168hrs PV is by far the more dominant force so we are probably going to be dependent on wedges coming into play on this run to help us, otherwise this could get bleak...

Only for high ground, looks like a classic hill snow chart to me, may be wintry showers might be another way to describe that. ECM once again proving why it is the king of the models, all the models falling in line with it...as I kind of feared...though as I've previously doesn't mean we won't get a cold spell, just a greater chance of a bust, that's all.

It should still be on the same general heading as the last few, so it may not necessarily be bad, but it does remind me a lot of the ECM 00z this morning with that flabby low preventing cold air coming down into a large portion of the country.

Models are looking very ECM 00z 'ish' at the moment out to 144hrs. Not bad but we need to watch the low pressure feature goes if we are to avoid something unwelcome coming in. Might not be the best of runs coming for the south, but too early to say!