At present it looks like starting around June 13th and running for some time after that. Plenty of 30c days to come based on current output. 

One thing I've noticed on some recent updates is that pressure quickly starts falling, so my hunch (and that's all it is) is we could be heading for a significantly thundery spell. (That's not hopecasting on my part because I'd much sooner have a long unbroken heatwave)

AIFS doesn’t look that convincing as low pressure keeps reasserting itself. 

Well let's hope it's wrong this morning because it says no to the heatwave.  Big wobble,  will the other models follow??

https://www.wetterzentrale.de/en/topkarten.php?map=1&model=aifs&var=1&run=6&time=198&lid=OP&h=0&mv=0&tr=6#mapref 

If this heatwave does happen its the biggest failure in the history of AIFS.

Game Over 

I think it just shows it’s as good or crap in equal measures to any other model

It's certainly struggled with this set up. 

As for the 12s so far GFS gives a 3 day heatwave before goes pear shaped but the AIGFS looks more prolonged. 

 GEM also looks like a 3 or 4 day heatwave but get pretty hot.

No, that would be the numerous times last winter it showed a hell of an easterly spell, doggedly clinging onto it even as the other models backtracked. The same applies to the AIGFS too.

That's the problem with the pattern matchers, y'see, they're matching the past rather than the present climate. It does, however, suggest we'd have had an absolutely cracking cold spell had we not had all that warming since the 80s!

Incidentally the MetO raw has 24 and 25 here for the weekend, 4 or 5 above average and with the usual sultry dewpoints too. GFS has the same highs and a sultry 28 on Monday, which is hot for the time of year - and above the 27 heatwave threshold.

It had a bad winter i agree but no worse than the other models.

But this is different it now doesn't have a heatwave at all, and goes mega unsettled soon after. If its wrong I've never seen it go this wrong before.

I just dipped into Manley's 'Climate and the British scene'. The climate he describes (it was published in 1952) is astonishingly different to now.

My guess is that AIFS is not wrong and we don't get any heatwave this time. 

Annoying but fascinating model watching. 

The return to unsettled cooler weather in my opinion will happen at some point later next week. The last week and this week so far has been awful and looks like continuing in the same vein till Friday earliest. I see the Met Office app has already downgraded Saturdays sunshine totals so we have to look to Sunday for an improvement if it is sun you are after.....

I just can't bet against AIFS even when its on its own. It's that good imo. Hope its wrong though. 

Other output remains much better for heat fans though including GFS, GEM and AIGFS all still show hotter, more prolonged and more settled weather.