Mike Poole

There’s a question mark in my mind over how this SSW will affect things going forward. I think there are two things with an SSW. In an energetic split vortex SSW, where the zonal wind doesn’t just touch 0 at 60N 10hPa but goes substantially negative and remains easterly for some time, that can downwell and affect the trop weather at our latitude over the next couple of months, maybe eked out in discrete stages. That’s not really on the table with this one, which brings me to the other thing, which is the lack of the strat vortex westerlies driving the trop pattern - it seems to me that’s largely been the case since the Canadian warming, and should continue. Which means, for me, it is up to the trop to drive the pattern it wants, unfettered from above. In which case, it is good that rising AAM and a favourable MJO phase might be driving the pattern into February in the direction of a -AO/-NAO, i.e. in a couple of weeks. But if that does happen, I wonder how much of that will be attributed directly to the effects of the SSW, and whether or not that would be correct…

ECM seems keen on some action. T240: Just appeared in last two frames.

The question is how do you get to a high lat block from where we are now. I agree with this. I think what we need to ask ourselves is, given the models were showing a rampant zonal pattern indefinitely, what is the first sign on the models likely to be - if the ultimate destination is a high lat block in Scandi, the first thing we will see is a mid lat block pushing north into the UK, pushed up by WAA from the vortex. If the vortex doesn’t relent, that should continue and drive the high to our NE - where exactly we don’t know, but a Scandi high looks a reasonable aspiration from there, given a more amplified pattern is expected from teleconnections.

Some support for the op on the ensembles, height rise through the UK looks probable, Perturbation developing the Scandi high T276: Promising…but a long way to go on this one yet.

Game on! GFS T318: There has been a signal for something on the way towards this on the EPS and clusters which definitely grew larger this morning. So very interesting to see GFS roll this out in FI this afternoon.

ECM clusters this morning show an increased signal towards something more blocked. T192-T240: Cluster 4 shows a ridge into Scandi, hints of that on clusters 1 and 3 too at T240. T264: The signal is maintained on clusters 1,3 and 5, although nothing yet resembling a true Scandi high. In fact, cluster 5 shows retrogression to Greenland in the last frame - but it only has 3 members, still it is a start. Clusters 2 and 4 show any ridge at T264 flattened by the zonal train. The signal for improvement in far week 2 are getting stronger (from a low base) and it will be interesting to see how/if they develop.

Plenty of uncertainty early doors on the ECM clusters this evening, then - from a point of view of looking for what might come after the Atlantic spell, here’s T192 onwards. Pretty much 3 shades of zonal until the extended, where once again, the signal is for a build of heights to the NW, most notably cluster 2. I was struck by the 46 Hovmoller plot tonight actually, there are clear changes suggested: You can see the Greenland block (upper B) collapse, to be replaced with a zonal period Z where things are clearly moving (diagonally on the diagram) east to west. But then there is a second blocked phase (lower B) which is transitioned to around the 25th January, with blocking just to our E. Later on than that there’s a hint of retrogression. This is the next opportunity for a chase into February, looks a bit earlier on the 46 than suggested by the EPS. But for now, enjoy the cold weather this week before the wind and rain returns. Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5013648

Plenty of uncertainty early doors on the ECM clusters this evening, then - from a point of view of looking for what might come after the Atlantic spell, here’s T192 onwards. Pretty much 3 shades of zonal until the extended, where once again, the signal is for a build of heights to the NW, most notably cluster 2. I was struck by the 46 Hovmoller plot tonight actually, there are clear changes suggested: You can see the Greenland block (upper B) collapse, to be replaced with a zonal period Z where things are clearly moving (diagonally on the diagram) east to west. But then there is a second blocked phase (lower B) which is transitioned to around the 25th January, with blocking just to our E. Later on than that there’s a hint of retrogression. This is the next opportunity for a chase into February, looks a bit earlier on the 46 than suggested by the EPS. But for now, enjoy the cold weather this week before the wind and rain returns.

Interesting! It is almost as if, since the Canadian warming, the strat has just been dancing to the tune of the trop, with a bit of a lag perhaps. And still is. It makes you wonder what might have been, with the strat vortex driver seemingly absent, what patterns the trop might have evolved into. 1963 is one, I suppose! The trop patterns (up to now, anyway) have been very unusual and I suspect the two things are connected. Instead we got a week long frosty spell. Ho hum! I don’t expect the SSW (if one it is) will do anything to help us, actually I don’t think it will do anything at all, not even downwell a bad pattern, if it continues to play like this.

ECM clusters from T192: For the T192-T240 timeframe, there really is nothing much to distinguish the four clusters for the UK, just strong westerly flow. In the extended, there is a tentative signal to build heights towards the NE, most notably in cluster 3, but that really is the only signal of interest for a change from the zonal dirge.

Yes, the 46 signal for February has been eroding a bit lately. I’m not as bullish about the February cold spell yet as I was about the current one. Don’t want to put too much store in the 46 because I don’t rate it, but one component of the idea of increased blocking potential is a decent amplitude MJO through into the favourable phases, and what is the 46 seeing: The moment it gets to phase 7 it goes directly to the COD without passing ‘go’ or collecting £200! We need to keep our eye on this, it may be just the vagaries of the 46, of course, but I think we do need assistance from the MJO to break out of this upcoming zonal spell. On the other hand the seasonal models bode well for February: Particularly strong signal on GloSea6, JMA and Meteo France, one proviso with those is they were run on or before 1 Jan, and we’ve had developments in the strat since then. Clusters zonal out for the foreseeable, T264+: Cluster 3 has a reasonable stab at a Scandi high, and 4 looks interested too - but note that this is at odds with the 46 and the seasonal which suggest heights would build to the NW not NE if anything. So a lot of uncertainty, hopefully some of this will become clearer soon, along with - well I won’t say fallout from the SSW (as will be one in name only as @bluearmy post earlier illustrated clearly) - further developments in the strat, shall we say. But at the moment I’m not going to be ramping February. Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5012267

Yes, the 46 signal for February has been eroding a bit lately. I’m not as bullish about the February cold spell yet as I was about the current one. Don’t want to put too much store in the 46 because I don’t rate it, but one component of the idea of increased blocking potential is a decent amplitude MJO through into the favourable phases, and what is the 46 seeing: The moment it gets to phase 7 it goes directly to the COD without passing ‘go’ or collecting £200! We need to keep our eye on this, it may be just the vagaries of the 46, of course, but I think we do need at least some contribution from the MJO to break out of this upcoming zonal spell. On the other hand the seasonal models bode well for February: Particularly strong signal on GloSea6, JMA and Meteo France, one proviso with those is they were run on or before 1 Jan, and we’ve had developments in the strat since then. Clusters zonal out for the foreseeable, T264+: Cluster 3 has a reasonable stab at a Scandi high, and 4 looks interested too - but note that this is at odds with the 46 and the seasonals which suggest heights would build to the NW not NE if anything. So a lot of uncertainty, hopefully some of this will become clearer soon, along with - well I won’t say fallout from the SSW (as will be one in name only as @bluearmy post earlier illustrated clearly) - further developments in the strat, shall we say. But at the moment I’m not going to be ramping February.

ECM clusters T120-T168: For the first time in ages, more than one cluster. Cluster 2 maintains some ridging in the Atlantic, cluster 1 has the more southerly jet. T192-T240: Various flavours of zonal, except for cluster 5 which only has 4 members and tries to build heights into Scandi. T264+: Both clusters start zonal, the first shows an inclination towards Scandi heights, the second shows an inclination towards an Atlantic ridge. Both signals to watch as we go forward, it can’t be both of them! Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5011258

ECM clusters T120-T168: For the first time in ages, more than one cluster. Cluster 2 maintains some ridging in the Atlantic, cluster 1 has the more southerly jet. T192-T240: Various flavours of zonal, except for cluster 5 which only has 4 members and tries to build heights into Scandi. T264+: Both clusters start zonal, the first shows an inclination towards Scandi heights, the second shows an inclination towards an Atlantic ridge. Both signals to watch as we go forward, it can’t be both of them!

It wasn’t a comment about teleconnections. While not infallible, on this occasion they did what it says on the tin, I agree about that. (The models, however, did overegg the blocking massively as this came into view which was an issue.) It is clear to anyone who has followed this winter chase for any number of years, that even with the right signals, it has become virtually impossible to get setups for significant snow in winter in southern UK. Apart from a few inches in December 2020, there has been no cold and snowy period since 2018 (does that even count as it was in the spring?). Changing climate seems to have done much more than increase average temperatures a bit, it also seems to have massively reduced decent patterns and altered patterns that once delivered into ones that don’t. This year promised decent patterns and has flattered to deceive so far. It may be many years before we get similarly favourable signals going into winter again.

I am increasingly coming to the conclusion that, regardless of what signals there are, naff all decent tends to come off!

Well that would tie in with what the 46 is saying, Feb: Not really interested in a Scandi block, but headed towards the seasonals’ signal for heights into Greenland w/b 12 Feb.

Yes, that is a worry I have. Say we do get a favourable pattern again sometime into February, it looks increasingly like a build from scratch job!

ECM clusters this evening, just one cluster out until T168. T192-T240: 6 clusters, but I think they group nicely into the odd numbered ones which are relentlessly zonal. Any southerly track to the jet is ironed out pretty quickly by the relentless flow pumping up height to our south. And then there are the even numbered ones, which show more than a hint of developing heights into Scandi - in transition from those heights to the south. This remains one to watch. T264+: And these don’t show any signs of that taking hold! Just dross without end.

UKMO still persisting with a much more amplified pattern at T120: That’s still quite a difference compared to GFS:

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?