There was someone from the WMO (John Nairn - Extreme Heat Advisor) on Radio 4 PM with Evan Davis this evening discussing the set up for these (almost) record-breaking temperatures across the N Hemisphere
He attributed the basis for this as the lack of sea ice / warming in the Northern Polar region leading to a very longitudonal jet stream around the globe in the north or as he put it "too many waves"
This leads to a very static pattern in which the peaks and troughs in the jet stream don't move all that much and consequently generate stuck weather patterns in any particular area. For us in the UK we are in a semi-static trough in the jet stream and on the northern side giving cool wet conditions but further east in Europe they are on the south under a ridge hence their long dry hot spell.
I think our long periods of alternating hot, cold, wet, dry months as the jet gets stuck in different set ups before moving to the next is evidence of at least a valid theory (but of course could be correlation not causation !)