Mike Poole

The setup for Thursday looks interesting, only 4 days away. UKMO has this at T96: Inside T96, I would back this model. But there are no precipitation charts, but looks to me like a good chance for the midlands towards the south east, details of course to be firmed up.

Quick comment on the 0z runs so far. Clean evolution to cold in the reliable, but showing a tendency for the high to collapse into the UK quite soon after, leaving a narrow window for snow. For sure there is potential afterwards, and I would suggest there will be a good month of weather coming often from the northeast quadrant, but of course it might be too late in the year for snow for many.

ECM clusters give no insight! Here for T72-T96 and T120-T168, there is just one cluster again. It does suggest that the guys and girls at ECM think high latitude blocking is going to be a theme going forward, but beyond that they seem to have no idea. Hey ho!

ECM T240: This looks to me like a locked in pattern for forcing cold air towards the UK. The Greenland height rise is now fact not fiction after the GFS caved in spectacularly today as predicted. The Arctic high is also forcing, and the remains of the trop vortex are now camped to our north east, just where we’d want them during winter . This all thanks to the final warming in the strat, which looks like an energetic event which we are feeling the effects of very quickly. Looking at the T850 chart, there is plenty of cold air that may come our way given the developing synoptic pattern, but it isn’t very cold, so any snow events will be marginal, but possibly significant. Need to watch the low pressure systems and the timing (day or night). April could be very interesting, I think….we will see…

It’s actually building towards a very unusual setup in the NH, here ECM T192: Greenland high, arctic high, and the remnants of the tropospheric vortex to our northeast. I think snow for some of us in April does stand up as a reasonable outcome, but of course time of day really important too now we’re past the equinox.

ECM T168: And what you can see here, is the likelihood of a prolonged period of cold weather from here, this is consistent with what I expect after the strat warming.

The Arctic looking down its nose at us (ECM T72).

ECM T120: Potential snow maker there for the south east if the timing is right vs uppers and time of day and all sorts. Potential all round but we need more runs to firm it up, but to me looks like the best chance of snow, better than all the extended autumn (I won’t degrade the word winter by applying it to the period from Dec 21 to Feb 22!).

ECM T72 and T96, was struck by where the air might come from at T72:

GEM at T120; We’ll take all you’ve got of those…

Yes, and if you look at the position of what is left of the vortex, it is of course reflective of the earlier strat explosive final warming, GFS T132: Which gives the opportunity for proper height rises in Greenland not seen all winter, and the opportunity for some snow here. And let’s not forget that this pattern might be with us for some weeks, as the strat final warming has thrown the dice in the air, and it looks like the UK may have them come down on the cold side…

ICON! Clean as you like northeasterly T120: UKMO good at same time: We wait for uppers…

GFS seemingly doubling down on the spoiler low it sees and no other model does on the 18z, here T90 compared to 12z T96: Told you it would take 3 runs, or maybe it’s right…..?

Yes, I’m expecting the same but with a slight shift. I’m expecting a reduced feature at T90 compared to T96 on the 12z. Part of the backtrack. Will post them when it is out, slow to start tonight, only out to T6!

Yes, looks a bit of a mess ICON, but that kind of solution is not off the table yet. It should be by GFS 6z tomorrow, is my expectation. But we don’t want a half way house solution here. I’m not that bothered what the pub run shows, great if it shifts now but experience suggests it won’t!, just UKMO and ECM to hold firm in the morning!

Just before the 18z rolls, a point to note. I have never seen the earliest chart T72-T96 of the ECM clusters have just one cluster! Until today: ECM rock solid on this evolution towards a NE’ly. And there’s more, just one cluster also through to T168: Looks like it is nailed on, just need a shift from GFS which I am confident will happen. After that it is a question of pinning down who gets the snow and how much…

So I think things are firmed up now on a cold spell end of next week, how cold and how much snow very much still to be decided. Model consensus on a northeasterly, uppers -6C or lower over most of the country at T168, with low pressure close enough for there to be precipitation either frontal or showers. Except for GFS. I’m of the firm view that the spoiler low that this model shows at T96 will not happen, for 3 reasons, the first the other models’ consensus, second it has a bias towards over-emphasising such features early in the run, and third - the stratosphere. I’ve not had my eye on the weather much this month, very worrying distractions elsewhere of course, but something significant has just happened in the stratosphere. Here’s the zonal wind chart from todays GFS 0z run: You can see the reversal of the zonal winds about 5 days ago. And remember this is on the back of an almost record westerly zonal winds all the winter season. It doesn’t look like the strat vortex will recover so it will be a final warming. But not one where the winds gradually shift to easterly by the summer, and have a benign effect. Quite the opposite, the forcing of this looks to me like it will be almost as strong as a SSW in the middle of winter. And I think we are seeing a very quick tropospheric response, about 10 days, 5 gone 5 still to come. You can see the alignment of what remains of the vortex, trop and strat in the ellipse profiles, T0, T192, to a location to our NE. (The ellipses for the higher parts of the atmosphere are not shown because the vortex is now not discernible there). So with all this going on, the GFS solution in the Atlantic just looks wrong. You may ask why I believe the strat charts which are also from GFS! The GFS has in my opinion got wrong a shortwave feature in the Atlantic, it is unlikely to have got the stratosphere and wider pattern wrong at such a timescale. My view is that the events in the stratosphere will result in a much colder than average April in the UK now. But effects of it will be long gone by summer, and - one for another post - I’m optimistic about summer weather prospects from, say, mid May. Back to next week. The question now (assuming GFS is wrong) is snow potential. More things in play now we’re in spring like time of day. And how close the low to our SE is to influence us. UKMO and ECM have uppers of -6C or lower across the country by this point, but the low pressure is much closer to the UK on the ECM, so that run obviously has more snow potential. Here T168: Should be interesting to see how the models firm this up.

ECM goes with the consensus at T96, the key time, and leaves GFS out on its own. It will surely backtrack, probably not straight away, might take 3 more runs, but we’ll have this sorted by tomorrow’s GFS 6z, I would guess. ECM and GFS T96:

Yes, the uppers would suggest that at T144, by T168, -6 or lower across the whole country: With the stronger sun now, time of day for any precipitation could be important, but enough instability around for something. ICON was slightly colder with low pressure closer, but that’s all uncertain at this range. Let’s see if we can nail the really cold uppers, and then think about what might fall from the sky.

GFS persisting with the spoiler low, no sign of it on the UKMO, T96: UKMO goes on to develop the northeasterly as per ICON.

One potentially snowy run from the ICON 12z for parts of the south here, T156: Let’s see what the others say this evening…

ICON 18z at T120, and a shift towards that cleaner route to cold, here compared with 12z T126:

A smattering of snow in November round here, then nothing at all through winter (some hail maybe). It is time we stopped calling it winter, it is just autumn 2 these days. I reckon decent snow in winter now ( for my area ) is about a 1 in 3 year event. So I’m hoping this ECM scenario will come off. After that, I’ll be all for sun and thunderstorms….roll on summer, but just give winter that one last chance!!

50p flakes from this I’d imagine for some, if the JMA 12z T168 is to be believed: My interest in the end of March has certainly been piqued by the current model output!

And continuing with the ECM clusters, that same 3 to 2 split goes on T120-T168, with the majority cluster 1 looking very cold for the UK: