Mike Poole

I’ve been wondering for a couple of days now whether we are starting to see the effects of the strat reversal now in the extended clusters: I think if we do, the likely area for blocking appears to be Greenland, as shown in clusters 2 and 4, maybe also 3 by day 15. One to watch, if this does happen it will be against the backdrop of the flabbier pressure patterns of spring rather than winter, and of course very late for any cold, but if the right pattern evolved, an interesting Easter weekend is still very much a possibility.

Well looking at the zonal winds, I’m don’t think the required 20 days has elapsed since the winds went back positive at 10hPa 60N after the last ‘SSW’, (19th Feb looking at this chart). So the upcoming evolution should be recorded as the aftermath of that SSW, not a new one. Which seems wrong, but I believe those are the rules.

Rain All Night I think it probably will return positive before a final warming in April. A period of reverse winds rarely lasts longer than a month, and so there’s still time left to return positive before the vortex peters out for the summer.

ECM clusters this morning T192-T240: Cluster 1 hangs on to a continental flow to the UK to T240, the others essentially a return to westerlies. The key thing seems to be the low out in the Atlantic at this time, if it is kept further west and shallower as cluster 1, then the block is stronger and the Atlantic held at bay. The zonal wind reversal in the strat has now happened, and the peak reversal about -14m/s expected in about 4 days - it will be interesting to see whether there are changes in the week 2 modelling as this goes through. If it is having an immediate effect, I would expect to see the block showing more resilience in runs to come. If its effect is still some time down the line, that probably wont happen.

ECM clusters T192-T240, there are just two options this evening: Interestingly, the rain fest of the GFS is in neither of them, so that model seems to have gone off on one this evening. Cluster 1 (contains the op, 32 members) stronger block, maintains the flow off the continent until T240. Cluster 2 (19 members) brings in a southwesterly flow courtesy of the low in the Atlantic. My impression is there’s still quite a bit of uncertainty but it seems to me like gradually, the runs with strong Atlantic influence are reducing or getting pushed back - slightly - it isn’t a strong signal.

Quite a difference as far as the UK is concerned by T168: The first low goes under according to GEM and UKMO, the next low, UKMO it’s a case of ‘to be decided’, the GEM starts to inflate it, the GFS is well on the way to a wet and mild thereafter. So UKMO this afternoon with the better block and cold option, with chance to add.

Very cold run, great alignment, from the GEM this morning, T180 GFS chalk to the GEM cheese! Small margins earlier make a big difference to the UK blowing mild or cold.

ECM clusters T120-T168: Support for the easterly on this timeframe growing, with clusters 2 (contains the op) and 3 - both take the low well south under the block. Cluster 1 more inclined to hold it out west, but this is the solution on the decline, I think. T192-T240: I think this timeframe is still work in progress! The UK rather in a no man’s land that could go one of a number of ways. More runs needed…

Rain All Night If each run takes 1 minute, 1000 member suites are easily possible…

minus10 Of course, we don’t know how long the AI model took to train itself to get to the point where it can knock out runs in 1 minute! And let’s not forget it requires as input the self-consistent T0 dataset calculated from the input data - that is a non-trivial calculation in itself which would take a lot more than 1 minute, it kind of gets that ‘for free’ as the main ECM models need it too.

ECM showing that there is potential in the upcoming setup. Close but no cigar at T216, but the potential to land something more significant is there before that. While I’m on, here’s the translated blurb for the AIFS model on Meteociel, for those interested: ‘These maps present data from the experimental European CEP/ECMWF AIFS model available in Open-Data. The maps are updated randomly according to the runs but generally one to two hours after the classic deterministic model is released. The resolution of the Open-Data model is approximately 0.25/0.28° (or approximately 25km/30km). There are fewer fields available than for the classic model. All fields are available up to 360h for runs of 00Z, 06Z, 12Z and 18Z. These data are provided on an experimental basis for testing forecasts made by artificial intelligence/machine learning, the calculation of the model by the AI is done in one minute (!). The model was trained with ERA5 reanalyses and classic ECMWF HRES runs.’ The model takes 1 minute to run - wow!

Good spot! It will be much easier to bring this into the discussion more if it is in the same format and with the same plotting variables as all the others!

ECM op well supported in the clusters T192-T240: It’s cluster 2 with 18 members. Fine margins with that high pressure to the north between the easterly and cluster 3 which has a southwesterly. Cluster 1 looks a bit of a mess. I still think the easterly may have some legs, it has shown for a while now, and like others have said, I think is has the potential to upgrade as the models factor in the details of the strat warming over the next week or so.

Met4Cast I completely agree. This winter was a major test for the new version of the 46 which, as well as running every day, also switched from being run as an extension to the EPS, to being run separately from T0 on a low resolution 36km horizontal grid. Which (I think) has actually contributed to its output essentially being reduced to noise long before the timeframe it is supposed to provide guidance on! ECMWF must surely have a rethink on that one!

Met4Cast February is a fail of epic proportions really. Whether your long range forecasting method of choice is the seasonal models, the ECM 46, or the GSDM, or ENSO, or the MJO, or the strat, (or tea leaves ), all of them at some stage (or indeed many stages) pointed to a decent spell of cold in February. The worst offender was the ECM 46 which persisted with it well beyond the point where everything else had given up the ghost.

Good post. However, the clusters are not a mean representation in the graphics. This, for me, is exactly the thing that sets them apart from other representations for the week 2 range. The graphics are from the representative member, not the mean. ECM website explains: ‘The most representative member of each cluster scenario is the member of the cluster which has the minimum difference from the RMS of all the ENS members in that cluster.’ Because it is an actual calculated solution and not averaged, it is therefore as physically possible as any op run.

ECM clusters again flirting with the easterly in the T192-T240 timeframe: Both clusters 1 and 2 take the low to the SW on a very southerly track, allowing flow from the east or southeast across the UK, or part of it. Together these are 46 of the 51 members. Still fluctuating suite to suite, to be honest, as yesterdays 12z had more mild solutions. You’d feel that with the strat situation as it is, the trend would against the Atlantic option, though. And as I said yesterday, if we do get the continental flow, it may require some patience before any significant cold air heads our way.

IDO The mean won’t verify. It can’t. It’s the average of many physically possible runs, but that doesn’t yield a pressure pattern that is physically possible itself. In this circumstance, it will be either one of the cold evolutions or one of the mild evolutions that have been showing on the op runs and the ensembles, and we just don’t know yet. I do think that if it went the way of the easterly, it would need to properly persist for quite a while to develop a suitable cold pool, with the reversal in the strat, that might not be as unlikely as it sounds.

I think a stronger showing for the easterly on the ECM clusters T192-T240: Both clusters 2 and 3 are now orientating the high more favourably, with the low initially SW taking a more southerly track, setting up an easterly flow in between. Cluster 1 has the low too strong and the high poorly orientated and a mild flow for the UK.

nick sussex Yes, the ECM is out of the same stable as yesterday’s GEM 12z. Would need some luck to land that - the thing is though, the winter cold-synoptics shield is switched off now, so at least we are in a fair game. Sadly, I never feel we are in a fair game when such things show themselves on the model output in January.

ECM clusters tonight, from T192 right through: It is cluster 2 (on both timeframes) that continues to provide interest for me, as this one could potentially draw some very cold air from the east/north east. The Atlantic low looks to stay camped west, allowing for the UK feed to be from a continental source. Cluster 1 also has blocking highs to the north, but never oriented such as to bring air from the east, and the UK is in mild air. Could easily go one way or the other here. The zonal wind reversal looks to be really quite severe now: The mean is bottoming out at about -18m/s. Expect the models to firm up on things a bit once the reversal happens about next Monday, the main effect of that to be seen in the trop may still be beyond the 2 week range, but something is suggesting quite a quick response in what we are seeing already - interesting times.

GEM 12z is up for a full on March cold spell by day 10: Incoming! I’ve been watching this possibility for a couple of days now, it’s been there on the ECM clusters, not favourite, but it is in the mix, and now on this GEM op run.

Met4Cast Means at that range possibly hiding some quite different options within a theme of a block to the north somewhere. Extended ECM clusters T264+ show this quite nicely: For the UK, all depends on where the block is and how it is angled. Cluster 1 (17 members) looks potentially quite cold. Cluster 2 (16 members) looks quite settled. The other two clusters have weaker high pressure with the UK remaining unsettled, cluster 4 in particular being mild.

GFS 12z going with the easterly that was suggested on the clusters this morning from day 11. T264: T312, and the cold air finally beginning to make itself felt.

Just perhaps worth watching a possible easterly setup around the 10 day timeframe. Clusters at T192-T240: Cluster 2 (25 members) showing more organised heights to the north, this was there in the extended clusters yesterday with just 11 members, so maybe an increasing signal. Some work to do to get from there to a proper easterly flow, the low to the SW would need to go under, or keep well away, and for any cold interest at this time of year, flow from anywhere south of east would not cut it either. But this would be post wind reversal in the strat, so worth watching as the models sort themselves out after that.