The GFS, as with heatwave 4, has been very bullish about another spell of mid 30s next week down here. For five runs in a row now it's shown low to mid 30s next Wednesday, and this morning is no exception. Here, for example, from Saturday onwards, the highs are 28, 32, 28, 26, 33, 36 - bear in mind 32 is exceptional here, or at least was until this summer! Even in 76 there were only 4 days in the 30s, and only one hit 31. As ever it's the lack of sea breeze which leads to those higher values being forecast here. The MetO raw is, as usual, much less keen (26, 28, 27, 26, 28) but I don't put too much faith in that given its poor performance this summer... it's regularly had a series of ninja-uppings as we've got closer to the day in question.

Another thing worthy of mention is just how dry the air is at times, reflecting that massive "heat dome" which has afflicted our region for months now. The GFS op has 28/-3 at Heathrow at 6PM on Saturday, for example, which is just 12.5% RH... more like you'd get on an aeroplane, or in a desert. The MetO raw has 23% on Saturday and several hours of 22% on Sunday for Heathrow.

The low humidity is important as it has several effects. A positive one is that it mitigates the heat somewhat if you get a breeze as it feels much fresher than normal (albeit you'll still feel it in the sun, in an area sheltered from the wind). The downside is that it'll dessicate things even more - trees etc will have to work harder, drawing even more on what scant reserves of water remains, and it'll make things even more flammable. I've called it desertification before and it's exactly what it is: at least we know in winter things will moisten up again, but for now it really is desert-like.

I suspect this coming heatwave will bring a flurry of 32s, perhaps a 34 or 35 or two, and it'll effortlessly add a further tally to our 30-degree count.

“Outlook for Saturday to Monday

A dry start to the weekend, with sunny spells the odd shower by Sunday. Turning warm on Saturday, but temperatures will slowly decrease into next week.

Updated at 4am today”

Yes, not for the first time the automated forecasts don't match the written ones - here it says,

"Outlook for Saturday to Monday:

Largely dry with sunny spells on Saturday and Sunday. In the sunshine it will be feeling increasingly warmer, becoming cloudy on Monday but remaining dry."

The automated, of course, shows full sunshine from dawn to dusk on Monday! In fact it shows completely clear skies, both day and night, from Saturday all the way out to Wednesday, which is as far as it goes...

As soon as Sunday GFS has us on 33c, and UKV on 34c.

It seem to brought forward the temps to go higher as originally Sunday was going for mid to high 20s after today.  Hope a sunny heatwave type like August 2022 did.   Like today hate those cool dry air mass that supposed to be cloudless like other time of the year on 20-21C temps. Some reason we cannot get sunny weather and below average temps as the clouds panic formed extremely early at 7am today.

App continue to undercook the temps but i expecting 29-30C Sunday and 33-34C Wed and Thursday as the 850s are 12C on Sunday to 16-17C Wed.

Hope Matty are on board of this heatwave this time because last time he was on board I got nice sunny weather on heatwave 1 to 3 but he walked away on 4 and 5 hence it been cloudy 2nd half of the day.

The GFS 6z has 35c on Sunday,  think it's probably over doing it. But 33c looks likely atm. Wednesday looks the best best for 35c. The GFS 6z has 37c and 8 30s in a row.

Arpege barely reaches 30C on Sunday, strangely. UKV also has a much cooler day on Monday.

There are still two discrete clusters for the weekend and Monday. One is the main GFS and AIFS solution, with hot air leaking up into Southern England; the other is the trough digging in and a temporary cool down before the heat builds back next week (though some ENS members have it never fully building back but sticking at 13-14C 850s).

Not totally convinced yet at all. Still seems to be a lot of short range model volatility rather and any overall consensus 

OK Brian. I think this one will be quite a dramatic one. There's lots of posts on it already. It was seeing the GFS which made me go for heatwave No6. 🙂🙂🙂

https://charts.ecmwf.int/products/opencharts_meteogram?base_time=202608060000&epsgram=classical_15d&lat=51.4673&lon=-0.4529&station_name=Heathrow 

One warm day on Sunday, too.

The 850 charts (plumes using the link above) show a 2-day hot push, contrast that with the 6z GFS which ups the chances (compared to the 0z) of a 4-day hot push:

https://images.meteociel.fr/im/52/4780/graphe_ens3rjp3.php.png 

My money's on the G(E)FS being closer to the mark, but we'll see...

It's interesting that you feel it's overshooting temperatures - I've felt it's often been a degree or two under. I've been taking a halfway point between the GFS and UKV and that seems to have been fairly accurate. 

It is and some said 35C on Sunday which is 3 days away, orginally was mid to high 20's.  Have to see on the next runs if they will pull back to high 20's or not on 12z.  06z ensembles show 15c here on Sunday, was 11-12C orginally before.