Mike Poole

ECM clusters looking much more promising this morning, T120-T168: The point of interest in this timeframe is the ridge starting to go up, notable on clusters 1,3,4 (not so much 2) at T168. It is crucial that this happens west of the UK in the Atlantic. T192-T240: Cluster 2 still has this ridge too close to the UK. Cluster 1 holds promise as regards building a well placed block to the NW, and cluster 3 is excellent - I think the JMA solution would fit well in this one - quite a turnaround seeing this within 10 days. T264+: Plenty of interest here, apart from cluster 1 where the block is too far west and the UK is in westerlies. Clusters 2 and 4 are exactly what we want to see as regards Greenland block placement and trough into Europe. Cluster 3 is OK, but dealing with the aftermath of the ridge through the UK earlier I suspect. Cluster 5 brings in the chance of an easterly with heights to the north more generally. Back in the game, this morning.

I reckon the JMA has this nailed at day 9 this morning:

I think we may see a lot of this sort of evolution over the next few suites, GFS T318: What I will be looking for is for the transfer of heights north to occur to our west in the Atlantic, rather than through Spain up through the UK. There is enough time for this shift to happen as the shenanigans associated with the SSW (if it occurs, still not sure) kicks in, I think.

Daniel* Yes, the way the strat and trop have been in step this year, it has been quite difficult to tease out what is cause and what is effect. Should the split vortex SSW happen, I would expect a very quick trop response, even to the extent of both impacts appearing to happen pretty much simultaneously.

Really interesting to see how AI forecasting develops. I’ve been impressed by what I’ve seen from the ones on the ECM website, astounding, actually, that they can even hold their own with the big NWP models. Presumably though, none of the pressure fields that they generate are actually constrained by the laws of physics? For the NWP, since they simulate the laws of physics (or their best approximation) all patterns generated are physically possible - that wouldn’t be the case with AI. Does this matter? If it gets the gist right, would people care? There must be a huge amount that AI could learn from the reanalysis data - but we wouldn’t get the understanding, just the output, who knows what teleconnections AI might discover but have no way of communicating to us. Fascinating new story of weather models, which we are only just at the beginning of.

Models at T144: Interesting differences in terms of the depth of the two upstream lows (marked 1 and 2 on the GFS chart). GFS has the first low more developed, therefore the WAA ahead of it, GEM the two are more equal so there is some WAA beginning ahead of the second one, and UKMO has the first one practically non-existent, which means the WAA will be further west ahead of the second one (we can check at T168). I think UKMO solution will suit UK cold prospects best.

Zonal winds down to -5m/s on the mean now: Reckon we probably need to see one of those bad boys plunging -20m/s or so, if a split like on GFS 12z is to verify. The SSW could still be a game changer, if we get a really favourable split, at the very least would take us into extra time, meaning that the exceptional synoptics needed to deliver in March, might actually be on the table for once…

ECM clusters T192-T240: Cluster 2 shows retrogression to Greenland from Scandi, maybe also cluster 1 to an extent. Cluster 3 continues to inflate a large high to our NE. Cluster 4 goes direct to Greenland and is the pick in this timeframe. T264+: Clusters 2 and 5 probably the best with a decent block to the NW. Cluster 1 could be OK with a tweak. Cluster 3 the block looks weak and cluster 4 has the ridge through the UK still. I had hoped these might be a little better than this, but potential remains.

GFS 12z T378, zonal winds at -19 m/s: Just wonder how much the big Russian high earlier in the run, and on recent runs, has to do with that.

feb1991blizzard Yes, well, this at the end! Completely smashed. This signal is increasing - and given how the trop and strat have been connected pretty much all season, I think the strat vortex never recovered from the Canadian warming, my bet is on a very quick trop response if this happens.

UKMO, GFS, GEM at T168: Big improvement getting that WAA in the Atlantic to the west, not over the UK or to its east. UKMO the pick in that respect.

GEM is very good, in comparison to recent output. At T240, the high is north of the UK and the retrogression pathway is on: Much better across the models this afternoon, hopefully recent op runs have just been a bad dream…

ECM clusters T192-T240: Cluster 2 looks decent with a block to the north. Not quite sure how this happens, though, because it is against the run of play, which the other clusters show is for mild weather, clusters 2 and 4 with high pressure nearby at T240. T264+: Much more uncertainty, so is the strong blocking pattern starting to disintegrate? (I’m kind of expecting it to, although for no good reason other than what can go wrong, will go wrong!) Well, clusters 5 and 6 emphatically go for the Greenland block. Cluster 3 does also, although it looks a little weaker, it is still well positioned. Cluster 1 is also blocked, but very unfavourably positioned. Cluster 2 high centered just north of UK at day 15. Which just leaves cluster 4 (8 members) with no appreciable blocking. So, as you were, the signal is still there, and we still have to get lucky re positioning of the blocking.

blizzard81 Let’s try and work this out, using the ICON run as an example. My thoughts are, is the whole thing behaving like one big complex low system? Here at T48 is our low: Then at T72, T96, T117 - does it make more sense if it is the system I’ve drawn in yellow?

damianslaw It is really weird. I am sure the models did have it heading SE a few days ago! Then the GFS got the idea of it heading NE, and now, particularly the GFS and GEM have it heading north or even NW. The thing is, it’s put a major diversion in the route to longer term cold.

ECM 46 zonal winds: Noteworthy chart because it shows a reversal on the mean. So it does now look like we’re getting another SSW. This one has a good chance of being a significant reversal. Will only add to the uncertainty… Except, I’m not sure I need the likes of ECM or GFS to work out how this is going to pan out. Oh, no! It’s perfectly clear that no sooner than longer daylight means that a decent snow event is no longer possible, the perfect cold synoptics will miraculously present themselves in time to ruin spring!

bluearmy T192-T240 charts to back up your comment: T264+: Clusters 1,2,3 all build a Greenland block formed by retrogression. On cluster 1 it is a monster stretching into the pole, cluster 2 retains some higher heights to our NE. On cluster 3, a white hole anomaly over Greenland results. Clusters 1 and 3 look cold for the UK, with 28 members in total. Cluster 4 is rather different with a westerly to the UK and Russian high. So, another day, and still jam the week after next. But the models really struggle in these setups that promise UK cold and then fail to deliver it…

Daniel* 1 hour difference there between the two plots might explain?

ECM clusters T192-T240: Cluster 1 demonstrates what has rather gone wrong with the output in the last couple of days, to build the high lat block, the ridge is through the UK, which leaves a build up of heights to the south and a lot of warm air that has to be shifted later. Cluster 2 has this further west, and cluster 3 further west still which is much better - low heights retained to the south and the block taking shape near Iceland. T264+: Clusters 1 and 4 make a decent fist of getting a northeasterly in by day 15. Cluster 5 goes a bit west-based. Cluster 3 holds some promise, cluster 2 leaves the block poorly orientated. Given clusters 1 and 4 total 23 members, I would say chances of getting a decent cold evolution within the next two weeks about 50/50 at the moment.

I wish people would stop declaring victory for the GFS (or the like) when neither its solution or that promoted (until this afternoon) by the ECM and UKMO has yet verified. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5030981

A look at the medium term evolution, from the ECM clusters, first T192-T240: The signal across the clusters is towards northern blocking. The presence of the high towards Russia probably tips the algorithm into assigning these as Scandi block (red border) as this weights the high pressure to the east of the Atlantic region, but the area that will affect the UK is more central on clusters 2 and 3, and to the NW on clusters 1 and 4. The concern though, as I mentioned this morning, is the fuel to build this high pressure tends to be from a ridge through the UK, so there is no cold incoming immediately. T264+: Cluster 1 has a Greenland high moving to Iceland. Cluster 2 has a Scandi high retrogressing to Greenland. Cluster 3 has a Greenland high drifting west. Cluster 4 has a strengthening Greenland high. Cluster 5 has a Greenland high drifting north. These are all rock solid consistent with the expected direction of travel from the 46 dayer, which still shows this today. We would be extremely unlucky not to get a substantial cold shot out of this, although, palpably, we do seem to be extremely unlucky this year.

I wish people would stop declaring victory for the GFS (or the like) when neither its solution or that promoted (until this afternoon) by the ECM and UKMO has yet verified.

ECM clusters T192-T240: The GFS solution at T192, in which the low clears away NE, is not really represented. Cluster 3 seems the most northerly track of the low. But the theme across all 5 clusters is blocking to our north. T264+: Both clusters end with a block to the NW, cluster 1 it is over Greenland but declines, cluster 2 it is to our N then retrogresses, with an initial easterly in this timeframe. Given the UK is very much on a gambler’s losing streak at the moment, one worry I have is that the high latitude block will prove to be a mirage - no evidence for that at the moment, but a concern might be ridge up to that does seem to pass through the UK on some runs, which would keep the cold at bay. So more detail as this counts down is needed… Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5030267

ECM clusters T192-T240: The GFS solution at T192, in which the low clears away NE, is not really represented. Cluster 3 seems the most northerly track of the low. But the theme across all 5 clusters is blocking to our north. T264+: Both clusters end with a block to the NW, cluster 1 it is over Greenland but declines, cluster 2 it is to our N then retrogresses, with an initial easterly in this timeframe. Given the UK is very much on a gambler’s losing streak at the moment, one worry I have is that the high latitude block will prove to be a mirage - no evidence for that at the moment, but a concern might be ridge up to that does seem to pass through the UK on some runs, which would keep the cold at bay. So more detail as this counts down is needed…

sheikhy I think it has been rock solid because it is erring on the side of its known bias to blow up lows, rather than disrupt them. The fact that the other models are seeing a shallower feature should not be discounted, I think it is likely that they are right and GFS has it wrong.