Decidedly dry air this morning in the South. Dewpoint is down to 9C already and I have a feeling it may drop from there.
Unlike some recent heatwaves this air is coming the dry route: up through a parched Spain, across the Pyrenees with a moderate Foehn effect, then across an unusually dry Central and Northern France that is in its 5th successive drought month. Plus Atlantic SSTs are very cold meaning less overall moisture in this part of the NH.
All this means I think we will see high maxes but relatively minima even under the 20C uppers - I wouldn't be surprised if we get nothing higher than a 19C min.
The 2003 heatwave in Europe was much more humid - hence I think the big death toll.
Brockley, South East London 30m asl