http://cdn.nwstatic.co.uk/gfsimages/gfs.20130726/18/165/h850t850eu.png
http://cdn.nwstatic.co.uk/gfsimages/gfs.20130726/18/165/ukmaxtemp.png
Closer to the ECM 12z op run from the 18z GFS op run.
Comes up with 33°C maximum but over a broad area that includes London - so a local 35-36°C would is not an unreasonable interpretation.
It's still a bit below the ECM values. If you take the areal coverage of the 20°C isotherm as a rough guide then ECM looks to be bringing 33°C+ across most of England, with 37°C or so in the London area... but only if the skies are reasonably clear! Continental thunderstorms could produce a lot of cloud to interfere with proceedings.
While the output is still at the sort of range where expecting an extreme event is foolhardy, I can't help but hypothesise about it...
The big deal about the ECM run is that the uppers probably cross 20°C across much of the south early on Thursday night, with a very hot and humid airmass easily capable of producing widespread 20°C minimums, perhaps a few degrees higher in major urban areas. From such a warm starting point, it's easy to see how temperatures could soar towards the record high levels - one could anticipate mid-20's by 7am in some places if it was sunny.
Now try to contemplate what conditions would be like under the region of 28°C uppers... dangerous for some. For this reason I can't wish it to happen, but if it does, I'll make the most of what I can while sparing a thought for those who suffer ill-effects.
Originally Posted by: Stormchaser