Captain Shortwave

Subtle changes on the output this morning, the surface high at least from what I can see that develops Friday into Saturday has disappear (especially on the ECM). As such the winds tend to remain from a southerly quandary and remain very light. The ECM again suggests that conditions will remain very warm/hot until Tuesday when fronts will push east. Again models like the UKMO disagree and push a weaker front south east and at an earlier timeframe. The GFS sort of sits between the two. I should add that the raw temperatures for Saturday and Sunday on the ECM 00z are higher than the values predicted for tomorrow and Thursday. 32/33c possible on both days after reaching 30c for a number of days prior to this. That is quite something.

The pub run is essentially a little warmer than the 12z on every single day in the shorter term. Sunday's chart now starting to show a bit more amplification like the ECM, though in this instance the GFS is close to pulling the 20c isotherm back over parts of the UK. Temperatures into the low 30s up to and including Monday. Whilst we talk about the warmth, this type of set up looks more conductive for thunderstorms as we engage the low west of Portugal that should increase instability.

The ECM operational looks a little extreme in developing that low and the slow eastwards track. ECM ens suggest a quick return to drier conditions, interestingly good support to redevelop the southerly at day 6/7 before low pressure wins out. Looks more like a blip and even the operational would return to fairer conditions after day 10.

Day 6 really marks where the models diverge again. ECM A general southerly flow for Sunday, again looks very warm or hot. UKMO Quite a bit flatter with winds from the west. It is still very warm in the south but fronts have made more progress. The ECM looks slower and more amplified. The GFS sort of sits between the two, the jet stream is flatter than the ECM, but the trajectory is further north than the UKMO, which results in most fine and very warm conditions whilst I suspect the ECM will generate a quicker breakdown but with a more substantial peak in temperatures potentially.

GFS 12z still only has a high of 28c for today (literally a couple of hours). Tomorrow - a patch of 30c across the Home Counties. Looks good for 30/31c somewhere south west of London. There will be a fairly keen east to south east wind tomorrow that might peg temperatures back a little in places. But

Well the ECM is a thumbs-up to this, the rest of the models slowly bring a front south east and take the cut off low out of play. Still uncertainty regarding how things pan out or indeed how high temperatures will be from Friday onwards. The ECM actually drops the temperatures by quite a bit on Saturday (looks like a cool undercut off the North Sea), but then rise through Sunday and Monday again. My point was mostly regarding to the chances of a plume developing during this coming weekend and into early parts of the following week. Probably 50/50 in that regard, especially as the operational appears to have decent support for winds from a southerly direction for Sunday/Monday as opposed to westerlies on the other models.

Typically one model decides to not follow the script and develops another southerly by Sunday and potentially into Monday too. The chart for Saturday and Sunday night Enough amplification and 850s still around 16c at this point. It is still possible that 30c could be reached for several days in the bounce but slight changes could affect what days this occurs and where in the UK it happens.

Well first day where conditions look very warm or even hot… and we start with thick fog. Luckily it is pretty shallow fog so hopefully it will clear quickly.

No secondary warm up likely now as the jet stream strengthens and slowly heads south during the weekend. Saturday looks decent for most but only the south hanging on to fine and very warm conditions on Sunday. It looks like a weak cold front will become slow moving over northern parts, though rainfall is probably going to be limited. Before then, Wednesday/Thursday still look good to hit 90F in places. Arpege going for 33c on both days, Thursday the hottest conditions look more widespread.

Typically like the reverse Midas touch, the ECM has lower temperatures for Thursday compared to the morning run despite lower 850s on that run and a more easterly element to the breeze. Reason - More cloud and some thundery showers move through central/eastern England during the early hours. That said the ECM now has a 30c across London for Wednesday (So again in the 32c maxima ballpark in reality). Conditions after Thursday look a little uncertain, some models keep that Iberian low in play, whilst others take it out of the equation, we also see a deepening low to the north that might impact how the high is positioned over the weekend, though there is agreement on a more westerly based pattern resuming beyond this point (Temperatures closer to normal probably remaining drier/warmer than average).

As it balances out this summer was okay, one excellent month, one poor and and one in between. However the way the weather ended up panning out, in particular the order of which those months came probably tells the story of why so many found this summer to be poor. June 2023 was exceptionally warm compared to average, but of course June is on average the coolest month and the CET of even this June only compares to a decent to good July or August. Secondly a lot of the worst weather occurred during the parts of the season that are average the warmest, even more prominent is that a lot of recent summers have tended to have the best weather loaded into July, so having a poor July was a bit of a shock. I think the last element is despite the very poor conditions seen at times during this summer, you didn’t have to go too far south to see your fortune change, so it was a little disappointing that at times some very hot conditions were merely a few hundreds of miles away, yet the pattern across the northern hemisphere was relentless at preventing even a weak ridge from veering the winds towards the south for even a brief period that could have landed a few more days in the low 30s maxima. Ironically this week may very well be a “This is what you could have had” moment where we seem unprecedented temperatures at 850hpa level across the UK. A set up during the summer could have landed another shot at hitting 100f, that said the very hot conditions across SW Europe have cropped up most years recently (The underwhelming UK summer of 2021 saw records fall further south for instance), so it wouldn’t surprise me if we see a chance of exceeding 35c next summer. Overall June - 8/10 - The first 9 days weee quite chilly and often cloudy (Though there were a couple of sunnier days or warmer days if the wind eased off), the rest of the month was excellent and very warm, though we barely scraped a 30c just once during this period. July - 4/10 - Rather poor but there have been worse, temperatures did reach decent values at times. One note was the weekend where Saturday was a write off, yet Sunday saw temperatures reach the mid-twenties. August - 6/10 - Poor start, a lot of pleasant conditions for a good part of the month, yet we were close to getting much more of it weren’t again for the long wave pattern preventing a more significant push of heat from the south. In the end I can’t really recall much from this months. Overall - probably a 5/10, there is a large weight put on the school holidays, unfortunately there were too Many poor days and not enough days that could offset this.

The ECM joining the other models in keeping the 20c isotherm across the south east up to and including Thursday. For Thursday, there does appear to be a bit of a breeze from the south/south east. Not much but probably enough to readily clear/disperse any fog. A set up like this should reach and potentially clear the 32c/90F mark. Of course the temperature charts with this will probably prove me wrong.

The 12z suite coming out now and an increasing chance that the 20c isotherm will remain in place across south east England for 48 hours (From late on Tuesday to Thursday evening), that is quite a synoptic feat, it is looking increasingly possible that we could reach 31/32c on both Wednesday and Thursday. Friday and Saturday will probably see a slight dip in temperatures as the high reorientates and briefly becomes more UK based before the high drifts eastwards again and we pick up a more significant southerly wind. Sunday will need watching in regards to how much there is in the tank for a plume event. The GFS looks pretty good for this.

Sunny all day here, the high cloud has tended to clear away and there is just a little fair weather cloud bubbling up. It should reach the mid twenties by mid afternoon.

The models seem less keen to move the highest 850s away from the east this morning, these remaining above 16c throughout the spell (including the weekend on the UKMO and ECM, the GFS does clear the 16c isotherm but it is only just across the channel and does try to move north as Atlantic fronts push in late in the weekend). As such there is an increasing chance of 30c being reached/exceeded for the end of the week and the weekend. I was for instance surprised to see a high of 31c widespread on Thursday from the UKMO (typically undercooks maxima on its raw output). For reference the high on Wednesday was 29c on this run.

Monday and Tuesday look set in stone, for instance the easterly wind on Tuesday looks to be quite strong in the south, it is a question of what happens Tuesday night when the isobars open up and winds fall very light. At the moment I suspect the arpege may be assuming widespread fog when in reality it will be patchy (usual areas like Fenland and the Vale of York) that see more of this and it clears quickly. Anyway the ECM has a high of 29c on Wednesday and 28c on Thursday, given the track record of the model this looks fairly in line with the GFS output. Again I think 32c is possible on Wednesday and 30c is possible any day from Tuesday onwards until the pattern breaks down (ETA unknown on that one).

Anyway back to the models, the ECM takes a similar route to the GFs with temperatures peaking midweek before the warmth ebbs away as we loose the strong influence of that initial Euro ridge. Conditions look mostly fine and very warm to end the week and through the weekend still. That said Sunday on the ECM could see the temperatures pick up again, whilst 850s are around 13/14c, the strengthening southerly breeze should help to lift temperatures back towards the 30c mark ahead of an approaching cold front.

That chart also shows temperatures reaching 24/25c on that day. The worst winds in the north west barely reach gusts of 50mph as the low ploughs into Iceland. So struggling to see the concern, especially as that is also 15 days away.

A couple of extra notes. Firstly the Arpege is definitely a take heed moment. The model predicts a high of 33c across south east England on Wednesday, however it also forecasts dense fog across a large part of central England that struggles to clear until the afternoon, as such parts of the Midlands struggle to reach the low twenties with areas such as East Anglia and other southern areas seeing temperatures between the two depending on how quickly any mist/fog lifts and clears. It is a bit difficult to split the fog patches from the low cloud towards the north east here. It does show the need to have some breeze from the south to really exploit the conditions. The second point is that the UKMO is stunning out to day 7 and would offer the chance of 30c being reached all the way through to the weekend.

Out of the days coming up, Wednesday looks likely that it could be the hottest day of the spell thanks to the winds generally being from the south/south east and still having 850s of close to 20c across the south. 32c looks believable given the set up, but you really need that southerly to allow temperatures to climb that high. Tuesday sees the peak of the 850s, but because the flow is from the east, this caps the highest temperatures a little bit (It wouldn’t surprise me if we still saw 30c though). GFS 850s Conditions looks pretty slack at the end of the week, the GFS has variable winds whilst the UKMO tends to keep a south easterly tug across the UK. Both solutions are likely to bring mostly sunny conditions with only a slight chance of a shower developing.

32c quite widespread on Friday on the GFS, that off the back of reaching 30c on the previous two days. Saturday also reaches the 30c mark on the 18z run. The ECM never gets that southerly going properly and as such the temperatures hold pretty steady (25-28c accounting for slight underestimate of maximum temperatures), the warmth lasts through the weekend albeit with conditions turning more unsettled as low pressure slowly moves in. Either way the output still suggests some excellent conditions to remind us that September is more than capable of surpassing the summer months in terms of summery weather.

GFS temperatures Monday to Friday; 27, 27, 30, 29, 29 (Could be a degree or so high come the day, for example the Arpege has a high of 28C on Monday and 29C on Tuesday) A very solid week. UKMO looks best at day 7 Looks like a much slower route to a breakdown, the warmth ebbs away on the GFS on Saturday, the GEM is a little slower with Saturday remaining very warm. For the record as asked above, 850s still peak around 20C towards the south east with the 16C isotherm still reaching most of England and Wales. Whilst nothing record breaking is on the cards, it is perfectly possible that we will see some of the best conditions on the year in terms of sunshine and warmth next week.

GFS slowly shifting towards the other models for the middle of next week onwards. UKMO There does seem to be scope for the elongated trough to deliver a much more meaningful southerly that could deliver hot conditions rather than very warm. Looks like 30c could be possible for both models on Wednesday. Monday and Tuesday have a high of around 27c across central/southern England on the GFS with mostly light winds and clear skies. Edit - Yep 30c widely across the south east.

The GFS has mostly clear skies on Monday and Tuesday with only parts of Scotland experiencing thicker cloud thanks to a frontal system straddling that region. The cloud cover is more extensive on Wednesday and Thursday but this is high level cloud and isn’t particularly thick, as such temperatures are similar to earlier in the week (26/27c).

Inversions are probably the biggest risk for high temperatures next week so perhaps shallow fog being slow to clear etc, but otherwise next week looks widely to be sunny and very warm. Raw maxima of 29/30c on the ECM should translate to around 32c (Not bad for September). Ideally we would want a little more breeze from the south to fully exploit the warm air aloft. The biggest disappointment is probably the timing of this, after a rather mediocre period for the school holidays, it could very well be the case that the first week back will be cloud free for many. Confidence looks pretty high for the next 7-10 days, potentially including a cold front moving east during the weekend following this one (but this looks weak and it appears the Azores high will just build back in afterwards).