kold weather

Still looking very much like a split, with the north not getting much apart from maybe Friday. The south, particularly in the SE will have what looks like a hot 5-7 days coming up. Arprge is back to 36c on Friday and it utterly nailed last Friday.

I think it comes from the fact that ECM and GFS both forecasted maxes around 32-33c and in truth most of the SE got at least a little high, and some got way higher. No certainty that happens again but the models nearly always push temperatures up as we move closer to the event.

The one big difference there is between the GFS and the other models is the LP over Iceland is around 5mbs deeper in the GFS than any other model around 36-48hrs out. May not seem a huge difference but that is just allowing the whole lot to flatten both a little faster and also pushes the heat that bit more SE, whilst other models are keeping the heat so close that even the smallest shift brings it back in, the 18z GFS along with the 12z run boots it well clear of our shores due to the whole complex being too far east. My guess is the GFS is overdoing that low in Iceland, that therefore means as the developing LP swings around the Iceland's lows base it gets further east due to being more dominated by the stronger low to its north (whilst that is not so much the case on the other models out there as the central point is more in the middle so to speak) and pushes everything that bit further east compared to other models. As said on the grand scheme of things not a drastic difference, but its got huge implications to the real world weather, especially for the SE of England and is the difference between 25c and 35c on Saturday.

Doesn't surprise me about Friday, the ECM has a relatively cloudy day on Thursday like Arprge and that does limit what can be done the day after, especially as it's not quite as extreme airflow as last Friday. As per normal, the middle ground is most likely the answer, with the closet to the south you are the better the chance of A: keeping the heat Or B: retapping into it if it does depart.

What I find with the GFS is its very prone to following its operational run, there isn't usually too much variance with it. Sometimes that pays off, but other times it can make the ensembles almost as useless as the operational in certain situations where the models biases are tapped into. Hard to know whether this will be such an occasion, though for sure it ticks the box of being overly progressive compared to other models at the same time, which is a well known problem for the GFS in blocking situations like this because it usually underestimates the extent of upper highs which in battleground type situations (which this effectively is) makes a large difference on the surface conditions.

Also the GFS seems really rather quick and progressive on shooting the heat east...however whilst many dismissing it, it is worth remembering the same already HAS occurred once, so there is a precedence for a quick heat up and then blast eastwards, no guarantee this evolves into anything more yet. Most other models thus far though suggest the GFS is being over keen in pushing things eastwards, and that is a well known bias of the GFS. It'll be interesting to see where it sits within its own ensemble mean.

ARPEGE is quite a bit cooler for Thursday on this 12z run, more in line with the other models. About 3-4c cooler than the 06z/00z run. I'm guessing Friday will be similarly cooler than it would have been, though still very much on the hot side of things.

My guess is given this is a late season heatwave the seas have warmed more compared with June and ground in France)Spain is warmer and drier, so you can probably get more with less. Thicknesses tend to support more at this time in the season as well compared to earlier on. It's kind of like a winter easterly. Rarely are they that great on November/December, but you can get some monsters in Jan/Feb as sea/ground temperatures adjust downwards and don't moderate the flow as much. It might also be that the higher resolution runs are showing higher 850 temps then we are seeing from the global models.

Yeah im pretty confident on a 36-37 on Friday, and probably Saturday, though the coverage of the hottest temperature may be a little limited to the SE quarter. Pretty rare to get two extreme bursts of heat like this from effectively two different setups.

Which despite the last few years is still a quite outrageous total that would solidly put in the top 10 highest UK temperatures ever. GFS parallel does appear to have a much better grasp on max temperatures from witnessing last week. It has raw 34-35c temperatures, probably somewhere like Heathrow sneaks a 36-37c in such a setup. To have possibly 3 days in the top 10 hottest ever come in the last 2 summers is a huge warning sign...and that's ignoring the 35c+ recordings from 2015 and 2018 and the 34.4c in September 2016...

Several pros and cons compared to last week, warmers ssts balance out slightly less energy from the sun. Lower uppers are going to be somewhat mitigated against by a little longer run up to the hottest stuff. If I was a betting man I'd say raw values seen on the models in terms of thickness and 850hpa temps probably support a local high end 36, maybe low end 37 but things could still shift either way.

Could well end up being a convective feedback issue, its certainly a problem with the GFS in the past in more tropical type airmasses and being a little overzealous with the instability actually present. It looks like it creates a decent thermal low which again maybe quite questionable to what extent that actually happens. Friday IMO probably is another 34-36C type day, of course IF we keep the flow going on Saturday and the uppers hold long enough, we will be in a position on Saturday in the SE to get somewhere close to the 37-38c we saw last week and also August 10th 2003. Regardless of what happens, I'd suspect the usual upgrading in temperatures to occur as we move closer to the time, and the current forecasts maxes of 31-32c to slowly shift upwards as the week rolls on. I'd be surprised if somewhere doesn't at least get to 35c given the time of year, flow over a now more reasonable temperature channel and also heat over Europe.

Worth noting that the ECM raw had maxes on Friday of 32-33c and that was clearly well too low. Watch the UJV and Arprge, they appear to have a better grip on maximum temperatures. My guess is not quite as hot as Friday, but I wouldn't be surprised if it ends up around the top 10 hottest days. Beyond Friday and huge uncertainty, unfortunately Isasis is going to cause real headaches over the next 24-48hrs for the models.

Imo GW does go a some way to explaining it. Land temperatures building upwards more than the sea will on average, but even the seas are warming at a decent clip as well. So the synoptics that used to deliver 33-34c now seem to deliver 35-37c type temperatures. There may also be argument that warming temperatures is forcing the subtropical belt northwards which is making south Europe drier and hotter in summer and makes it far easier to tap into that heat synoptically, so what would have previously been heat that wouldn't make it past France before skewing off eastwards is now close enough to on occasion punch into the southern half of the country.

I think what was different today was the timing was a little better than most recent heatwaves. Even the record last year was a little surpressed as light showers/cloud started coming in as early as 1-2pm in the SE where the highest potenial was (hence why Cambridge region got higher in the end). Today, we got little cloud until after peak heating so unlike 2019 and 2015 heat plumes I think we got right upto the theoretical max we could today with the set-up aloft. With both 19 and 15 I feel there was probably another 0.5-1C to be squeezed out of the set-up.

Definately got the looks of a possible heatwave, though caution should be had that this whole set-up is still a ways away in the grand scheme of things and it wouldn't require too much of a shift SE to put the UK back into the cooler set-up around the south-east side of the upper low. Also, hurricane Isaias may well prove to be a wildcard here depending on the exact track and how much land interaction it ends up having....both in a good or a bad way in terms of any heatwave in the 5-10 day range,

I did think there was a chance of a top 3 finish today based off of what you s really impressive thickness, decent uppers and prolonged sunshine (in recent times such shots have ended up cloudy by 1-2pm.) Still, it's a bit surreal that 3 summers in a row have gone 35c+ for maxes, and each one impressive for different reasons.

Amazing really, Im guessing we are now in top 10 territory, maybe even close to top 3 by the end of the day. Really telling that this is the 3rd summer on a trot with an absolute max above 35. Another clear sign of a warming climate. It feels like we've seen another stair step up in terms of how easily we can tap into this 34-36c type air, almost as easy as it used to be to get 32-34. A 40c can't be super far away, we already know we can theoretically reach around 42-43c (the atmosphere was warm enough in June 2019 heatwave, just wrong surface flow scuppered it.)

Likely to get to 37, going to a close call as to whether we breach 100f.

Really interesting evolution yesterday which meant it beat the odds against Hispaniola. The whole southern vortex opened up as it approached land and as the MLC moved offshore further north a surface low formed along with it. The frictional effects of northern Hispaniola actually then tightened the new low and consolidated its southern flank. This combined with a favourable shear motion helped to really kick this thing off and has continued to support several large hot towers blowing up along the shore of Hispaniola. Not uncommon to see this happen to storms however it is rather for Hispaniola to create internal changes that support development, this was about the only possible evolution that could do that.

The next 5-7 days looks about as rough as you could get for the time of year. Still pretty much peak insolation with a strong high pressure aloft, little cloud and decent warmth spreading across much of the Arctic. I think any idea that this summer will be a recovery summer compared to the last couple looks very unlikely now after a relatively ok May compared to recent years and ok previous winter.

Looks like it's just a thundery band of rain with the odd embedded cell at the front and back edge. Could be more cells behind that come up very early hours but I'm not all that convinced for the south sadly. Others are doing better though further west/north today.

Yes another cell seems to be going up on the eastern flank. Suspect this will be one of those nights where some will get a decent show and others will get some moderate-heavy rain and thats it. Classic potluck with embedded convection within a larger region of rain.

That first band has the look of thundery rain to me, the odd bit of thunder here and there but mainly moderate-heavy rain. Hopefully it perks up a little again and at least there is some embedded cells still firing as it crosses the channel. I've got a pretty prime view to my south as the night draws in, anything electric that does start to kick off is going to be pretty easy to spot in a semicircle expanding out as much as 70-100 miles from me to my south.

TD3 is now here, has got a classic gyre look to it that you see in these EPAC/BoC type systems which throw out multiple systems, this gyre has now produced 2 such systems. IF Td3 goes inland don't be surprised to see it pump out a further storm, the GFS and a few other models have been showing just such formation IF this one does dive inland. I see no reason why this won't be our 3rd named storm, an d several days in front of the current record holder of 2016. 2 early storms don't tend to mean much statistically, but 3 early storms tends to put the weight towards a more active season, especialy if one of them is from a pure tropical source like TD3 is.