I suppose the question is what counts as “double”. Mid 30s I would guess.
In some years the double scenario would imply hitting 30C. That’s just “more of the same” in the 2018 context.
This year is a really powerful example of soil moisture feedback, both on rainfall amounts and daily maxes. The gap between 850hPa and surface temperatures has regularly been as much as 18-20C. I had always used a rule of thumb of 17-18C in strong sunshine, in midsummer, reducing to 15C by late August.
Originally Posted by: TimS