Mike Poole

Others will be able to answer this better than me, but I think the fall in AAM generally recently (plus a lag) is probably responsible, here’s the recent trajectory: It was positive, but has now fallen back below the half way line, so we’re kind of playing in our own half of the field at the moment! Personally, I’m not 100% sure how that relates to the MJO, some have bigged up the amplitude in phases 2 and 3 as being helpful, I’m not convinced, but we’re in phase 3 at the moment, and forecast to go through phases 4 and 5 (which aren’t helpful) but we’re not there yet and there is a lag too, as I understand it.

Unfortunately, it seems to me (see my post in the strat thread) this SSW (if it happens) seems to be caused by the exact pattern in the troposphere propagating up - so I can’t see it changing anything in the way a normal SSW might - it seems to me to be part and parcel of the current evolution, which, as we know, is not headed in a good direction. I think the next chances have to come from trop drivers - the benefit of the SSW is that should we get them, the weakness of the strat vortex should accommodate them, rather than resist them. I don’t see the SSW being the direct cause of any major upheaval down here, I hope I am wrong about that!

Day 15 toppler the extent of ambitions now is it?

ECM extended clusters this morning do not bode well, T264+: Choice of zonal, zonal, zonal, zonal or zonal, take your pick!

Yesterday’s ECM 12z, technical SSW at T96, with reversal 60N 10hPa: Seems to count as a split, however short, and it’s come from the trop up, you can see it at 50 hPa T0, 30hPa T24, 10hPa T72 and 7hPa T96: Unusual to say the least, my theory is that it is down to the Canadian warming in early December which caused such a significant weakness in the strat vortex, that it didn’t form properly, and that has allowed the amplified trop patterns to do things they wouldn’t normally be able to do, such as propagate splits up to 10hPa. And finally (maybe) register a technical SSW by the bottom trapdoor. What are peoples’ thoughts?

ECM clusters tonight, just one in the really uncertain timescale T120-T168. Then the computer’s come up with this to T360: Pick the bones out of that! I’ve not given up hope that the models have not yet got the early evolution, but will comment on it now by exception if anything interesting happens. The transition to something milder was always suggested for the last week in January, so no problems with that. It would be nice to see some proper snow during the cold week to come, but it doesn’t look like it now. There is interest into February when we will get another crack at it, and there’s a probable SSW in the mix there too, and although it looks a weird one to me, it could certainly help in the period into February when a more amplified trop pattern might well be expected. With both in mind, I actually think there’s a chance the next chase might be for an easterly, which albeit rarer, has more chance of delivering, we will see…

Yes, but not to the extent that there was on UKMO. Still, this one might not head towards some kind of horror show vortex of doom by day 10, so let’s be thankful for small mercies.

That’s my intuition too. Although the other models need to get a march on if it is right!

UKMO T144 rather a lone voice now, in keeping the ‘lobe separation’ this far:

It does, maybe heading for the snowless breakdown I joked about the models seeking out yesterday.

The new ridge being thrown up does not on this ICON run connect with the Greenland high, but we are still in a northerly T138: Interested to see where it goes from here.

Agreed, ICON would reinforce the ridge via WAA shown and go down the cluster 1 route of extending the cold, here T120: GFS same time, that ship has sailed and the ridge is collapsing: I think ICON is right here, and predict this will show more strongly on the 12z runs.

ECM extended clusters T264+: If we recall in the previous timeframe the majority cluster 1 rebuilt the ridge - to do this it needed some WAA into Greenland, and this came from developing a powerful system on the ESB. Not really focusing on details here, because lots of runs in this have probably got the early evolution wrong, but the trend here seems to be for that system to move east, and push up a ridge ahead of it, you can see on clusters 1,2,3,4 - but you can now see how this could end up as a Scandi high, cluster 4 the closest. If the earlier cluster 1 was right, one might expect this signal in the extended to get stronger. Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008275

ECM extended clusters T264+: If we recall in the previous timeframe the majority cluster 1 rebuilt the ridge - to do this it needed some WAA into Greenland, and this came from developing a powerful system on the ESB. Not really focusing on details here, because lots of runs in this have probably got the early evolution wrong, but the trend here seems to be for that system to move east, and push up a ridge ahead of it, you can see on clusters 1,2,3,4 - but you can now see how this could end up as a Scandi high, cluster 4 the closest. If the earlier cluster 1 was right, one might expect this signal in the extended to get stronger.

ECM clusters - just one cluster until T168, which is the timeframe that is really of interest, so once again there is little they can tell us, but T192-T240 does show something interesting: Which is that cluster 1 does retain/rebuild the ridge! And maintain lobe separation. This, IMHO, is the direction we should be looking in. Cluster 2 contains the op and is more mobile for a time, and cluster 3 is the more southerly tracking jet option. Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008234

ECM clusters - just one cluster until T168, which is the timeframe that is really of interest, so once again there is little they can tell us, but T192-T240 does show something interesting: Which is that cluster 1 does retain/rebuild the ridge! And maintain lobe separation. This, IMHO, is the direction we should be looking in. Cluster 2 contains the op and is more mobile for a time, and cluster 3 is the more southerly tracking jet option.

Just catching up this morning. Focusing on ‘lobe separation’ first - I still think the right solution keeps the vortex lobes apart for longer - so UKMO and GEM do this this morning, GFS loses the plot rather early, and ECM is quicker to phase the lobes as well this morning. GEM then goes on to descend into ‘scribbles’ (as @Tamara aptly described yesterday’s 12z GFS!). This is all saying that until this part of the jigsaw is put together early doors, the later part of the runs is really just pure speculation, and that includes most of the snow risk, and especially the incursion of the low from the SW. We just don’t know yet. It does all depend on how long the lobes stay apart, if longer, the cold will penetrate further south and there will be no battleground as the low goes through France. I see this as more likely, perturbation 17 () has this idea at T168: At the moment, most runs have collapsed the ridge by this point, though. If that happens, then the low to the SW may track further north and provide snow as it runs into the cold air, longevity will then depend on how much cold air has got south by that point. Plenty still to be resolved.

Yes, that’s my view too - it is coming to the crunch now. For this time period, the models have been flailing around in the dark for days, but now the changes we are seeing day 4 to day 5 have to be the models starting to home in on the final solution.

Strat is toast on this one, T234:

T96 is pushing the edge of the reliable at the moment. Beyond that, I think we will continue to see this trend to keep the vortex lobes further apart on the 0z runs, and the further evolution after that will continue to change. Which will be an upgrade in terms of depth of cold, that we can see. Snow chances will be different because there won’t be a battleground scenario at all next week, is my prediction.

GFS T114 v 12z T120: You see what I mean about keeping the lobes of vortex apart? Much stronger ridge on this one, as per ICON. I see Si just beat me to it

Would have liked that one to have run longer. Just starting to hint at keeping the lobes apart a bit longer there at the end, which is kind of what I’m expecting to see. Don’t think we’ll see it on GFS, as that model is still a bit behind the curve in my view, but maybe on tomorrow’s 0z runs.

I think if we get a technical SSW, someone will more inclined to do some proper research as to what the hell happened up there this winter! Agree, that double dip is interesting, as you say, with it being trop driven, I don’t think a recovery to average zonal winds in the strat is a done deal.

ECM clusters tonight. Once again only one in the T120-T168 timeframe, which for me is now the key one - so regard subsequent output as suspect as we’ve no guidance on that from the clusters! T192-T240: The op is in cluster 1 which just holds off the coming together of the west and east lobes. Clusters 2 allows the cold deeper south as far as I can see. Cluster 3 seems to go west-based. T264: Clusters 2 and 3 both suggest a possible route to a scandi, 3 closer to it than 2. Cluster 1 looks mobile but drags a ridge up in the vicinity of the UK at the end.

JMA clean at T96 too: Similar evolution to ECM after, possibly more snow. I think we are now in a good position at T96. But I think the period T120-T168 is not yet nailed on any of the models. I think the move to deflate the ridge and close the separation of the two lobes is overstated by the models, and will maybe take place slower or even not at all.