Mike Poole

Uncertainty Yes, I agree, the models are suggesting this could turn into a spectacular late winter cold spell. I think, perhaps, posters on here invested too much in what was a very long chase for something very mediocre in January, and are perhaps being over-cautious second time round. GFS 6z has this at T270: Very consistent with what the ensembles are saying about expected developments to our north on this timescale. It would be very unlucky to miss out on some memorable winter weather from this, will be fascinating to see how it pans out.

ECM clusters not holding back about the longer term evolution this morning! T192-T240: Blocking developing during this timeframe, strongest into Greenland in cluster 3. Northerly component to UK winds on clusters 2 and 3. Cluster 1 builds the ridge through the UK to the NE, with a ridge to the NW as well. T264+; Worth looking at the big picture across the clusters. A diffuse pattern of blocking at day 11 converging on strong blocking in the Greenland area by day 15 - on all clusters. Although, interestingly the 4 day 15 charts all have different coloured borders, so the algorithm has seen fit to classify them as different regimes! If anyone can explain why the day 15 chart on cluster 2 is +NAO, and on cluster 4 it is -NAO, please tell us! There are differences in the exact placement of the high, but the detail of that won’t be resolved for a while.

Concentrating on the medium range timescale, and the development of high latitude blocking, GEM already showing signs at T240: GFS a slower burner this morning, but well on the way there now at T330:

GFS 18z settled on a UK high for a while, but at T360 - surprise, surprise - it’s now on the move! Think we’re going to see some fascinating evolutions in FI over the next few days before the models converge on which one is actually going to happen, but all the signs now are that we have a real chance of nailing a proper cold spell.

ECM 46 looking good re pressure patterns. Zonal winds: Fewer members today going for the technical SSW than yesterday. This chart suggests we’ve made it into phase 8 on the actual data. The model would have us back in phase 6 by day 5, but I remain suspicious of that!

ECM clusters, T192-T240: Custer 2, which contains the op and has 22 members shows developing high pressure to NW possibly linking to NE. Cluster 2 a modest wedge of high pressure, but well placed. Cluster 3 similar to NW, but a low camped west tending to re-inflate Southern Euro high. Cluster 4 heights getting sucked north through the UK. T264+: Er, just bank, please. All of them! Clear trend to a northern block, clusters 1 and 2 centred south of Greenland, cluster 2 has NE’ly over UK. Cluster 4 extends the high east and brings in easterly. Cluster 3 just drags its heels with surface high pressure close to but west of UK. Major upgrade tonight!

Just seeing a subtle change around day 10 in the models tonight which could have positive ramifications. After the low has passed, there is a tendency for the high pressure that follows it to track to a slightly higher latitude, which means that instead of the UK high which was seemingly the destination days 10-12 in recent runs, a block further north of that is now looking more likely.

Eagle Eye Yes, GEFS 6z have 58% chance of a SSW now. In an ideal world, the QTR from this will kick in just as the lagged AAM/MJO response is waning and ignite a BFTE 2024…well, it could happen, couldn’t it? Or, for balanced commentary, the SSW could demolish a perfectly placed block established as a result of the AAM/MJO. Something to keep an eye on, as you say…

Where’s this high going? GFS T270: If you accept that potential for Thursday’s snow is confined to the north, then moving on, the next phase is the surge of cold south as the low passes - this looks good on both GFS and GEM this afternoon. And GFS heading for a decent finish…

Met4Cast I see what you are saying, but I do think sometimes the teleconnections view is always on to the ‘next thing’, before the current thing has had a chance to play out, the lagged response to which is what the models are currently struggling with out in FI. It has not yet been resolved as to what the local UK impact of this might be. Too early IMHO to call this a bust. (And there is still a possible SSW around the 16th which may further complicate things.)

LRD Yes, bear in mind the regimes are for the Euro-Atlantic region, which the UK is towards the east of. So the red would include a mid latitude UK high as well as a high centred over Scandinavia regardless of what the description says, and indeed, in summer, the desirable (for most) charts are those with a red border.

ECM clusters are back after going AWOL last night. Only 1 cluster out to T168, so no light to be shed on the potential for snow in the next week, and to be honest the op runs will be a better guide to that anyway. T192-T240: Cluster 2 looks cold for the UK, with the trough extending way south and a wedge of heights to the NW providing a northerly flow. Cluster 1 has stronger heights to the NW but more distant, and the trough is less pronounced, but still a cold evolution. T264+: There is a lot going on here. One thing that strikes me is the amount of red borders (Scandi block). This highlights the possibility of drawing in an easterly or northeasterly. Cluster 3 shows this well - evolves a very well placed block. Cluster 2 could be good too with some tweaks. Cluster 1 heads the block up to Greenland, again slight tweak needed to align with the UK. Cluster 4 has a much weaker attempt at blocking that largely fails to take hold. Plenty of cold options in the mix in the extended timeframe. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5028583

bluearmy According to ECM, on the cluster plot: a red frame indicates association with the blocking climatological scenario, a blue frame indicates association with the positive NAO climatological scenario, a green frame indicates association with negative NAO climatological scenario, a violet frame indicates association with the Atlantic ridge climatological scenario. The same colours are used on the 46 dayer regimes plot, where they are described as follows: Blue - positive North Atlantic Oscillation (NAO+). Green - negative North Atlantic Oscillation (NAO-). Red - Scandinavian Blocking (BL). Purple - Atlantic Ridge (ATR). Grey - members with no regime attribution Assuming the regimes are the same or close, then I think it is right to interpret red as Scandi block, but obviously each regime covers quite a wide range of possibilities, and sometimes the plot doesn’t obviously look like the regime it has been assigned by the algorithm! In fact, one could simplistically interpret the regimes as: blue - high to the south, green - high to the north, purple - high to the west, red - high to the east. And that wouldn’t be far wrong.

ECM clusters are back after going AWOL last night. Only 1 cluster out to T168, so no light to be shed on the potential for snow in the next week, and to be honest the op runs will be a better guide to that anyway. T192-T240: Cluster 2 looks cold for the UK, with the trough extending way south and a wedge of heights to the NW providing a northerly flow. Cluster 1 has stronger heights to the NW but more distant, and the trough is less pronounced, but still a cold evolution. T264+: There is a lot going on here. One thing that strikes me is the amount of red borders (Scandi block). This highlights the possibility of drawing in an easterly or northeasterly. Cluster 3 shows this well - evolves a very well placed block. Cluster 2 could be good too with some tweaks. Cluster 1 heads the block up to Greenland, again slight tweak needed to align with the UK. Cluster 4 has a much weaker attempt at blocking that largely fails to take hold. Plenty of cold options in the mix in the extended timeframe.

Moving south at T156: Just shows that there is a chance that large swathes of the country could get a good dumping from this, and within 7 days.

No sign of the clusters this evening. ECM 46 has a few points of interest, here’s sea-level pressure anomaly: Signal remains for high pressure to the NW until mid March. But where does it get the Greenland high for w/b 5th Feb from? Zonal winds: Again an increase in the cluster going for an SSW around 16th Feb. MJO: This is a slight concern - for days the actual MJO has verified more amplified than the model predictions consistently. But there is little signal in the model to now move it into phase 8 with any amplitude, do we keep the faith or will it fall at the final fence? (It has form for this!)

GFS 12z has another strong reversal in the strat, -14m/s by the end: This is gathering momentum, the impact of this would most likely felt be towards the end of the month, but the GFS 6z responded very quickly from the top down:

Cold Winter Night That’s a very good point. Any snow end next week would be a bonus that has never been guaranteed, it is possible with the right wedge/slider combination, but the real interest, and what the teleconnections, and ECM 46 have been suggesting begins w/b 12th Feb. I am with others in having the jitters about all that getting downgraded before it reaches the reliable, but as yet there is no specific reason why that should happen other than Sod’s Law (which has tremendous forecasting accuracy when it comes to UK winters, it has to be said).

GEM the pick this afternoon, brings in easterly nicely, T204: GFS is good also, cold is delayed compared to the best runs yesterday I think. UKMO poor again (and bear in mind the majority ECM cluster favoured it). Snow towards next week end still very possible for some, I’d like to get that nailed - there are likely to be good opportunities to follow, but in the UK those cannot be taken for granted yet. Still uncertainty over the MJO and whether it will make a decent phase 8 that I’d like to see resolved to have confidence that the consistent longer term forecasts from e.g. the 46 will deliver.

GFS 6z has very nice wedge at T144, helps the cold flood south by T180:

ECM clusters T120-T168: Looking at the T168, they differ in the position of the trough, cluster 1 has it west like UKMO (21 members), cluster 2 goes with the op (17 members) and cluster 3 has it deeper more like the GEM (13 members). T192-T240: Here, cluster 3 (16 members) has the most northerly line of attack with a deeper trough. T264+: Cluster 3 is the one we want here (16 members) with a very good strong block in a great position. Cluster 2 develops a ridge in the Atlantic and pushes it too far east, cluster 1, despite being -NAO retains a westerly flow to the UK.

GFS is able to bring in an easterly T246: Initial cold plunge delayed a little on this run compared to 12z, but an interesting evolution so far afterwards. There are quire a lot of options for a cold evolution beyond day 9, I think.

ECM 46 increasing the chances of another SSW just after mid month. We’ve seen a reversal on some GFS runs too. The main cluster remains centred on a reduction to 15m/s as it has for a few days. Will be interesting to watch, because of those that do show a SSW, some have the zonal winds going negative big time. Just another variable in the mix here, and given how closely the strat and trop have evolved all winter, one would bet on a quick trop response of one of the more energetic SSW members came off.

ECM clusters T192-T240: The genera trend clear across both clusters is the Euro trough and a high west of Greenland. Cluster 2 has more of a wedge in the Atlantic meaning that the trough is sharper in the vicinity of the UK through day 9. T264+: An explosion of uncertainty at the extended range. Cluster 5 brings in an easterly under a block through Iceland in to Scandi abd is probably the pick, cluster 3 looks a return to westerly. Clusters 4 and 6 have a northerly ahead of ridging in the Atlantic, in cluster 4 extending to Greenland. Clusters 1 and 3 look a lot going on with wedges and so on, would be useful to look at in-between charts as things are moving. As I say, a lot of uncertainty to resolve, but all with plenty of interest.

Harsh Climate There’s two things in play now, one is the wedge (or not in case of ECM) and whether that will result in snow in just a week’s time - and if so, where? I think that is a separate issue as to the longer term evolution (Euro trough and blocking to the NW) but if the wedge verifies it will certainly help bring the Euro trough a reality sooner. But it should happen anyway, in the no wedge scenario, the models will just find another route if that destination is the one driven by the background signals. ECM T216, and the northerly is in, courtesy of the flimsiest ridge to our west imaginable!