The fax charts show a 'cooler' pool of upper air sat over England and Wales on Monday in tandem with a decaying front. Then slight cooler air pushing south east on Tuesday.
You'd normally expect the situation shown on the fax charts coupled with the sharp decline in temp forecast for Wednesday-ish to produce some juicy thunderstorms - but none of the models or forecasts seem to be buying into this (just one of the ens runs for e.g. Brighton has a rainfall spike this week).
The heat wave is dead by next weekend with cool NW air (GFS) even assisted by the remnants of a hurricane (ECM) though there is a recovery later. A few ens runs manage to keep the warmth going, especially in the south but the majority are below average.
War does not determine who is right, only who is left - Bertrand Russell
Chichester 12m asl