The trend to warmer uppers is well supported and at short notice. Of course conditions at 2M will be highly affected by cloud cover so extrapolating increasing uppers can have variable results as we head away from solar maximum. It won't be cold though.
Originally Posted by: Sevendust
Indeed, I think some people are looking at 15C 850s and assuming a hot spell as a result - which would be the case if we were still under the heatwave pattern, before the heatwave broke.
As you say, however, there's likely to be more cloud around and as we approach 8 weeks since the solstice the sun is now having somewhat less of an effect on heating; those looking for hot weather would rely more on importing heat than cooking up our own.
The 0z EPS suite shows this well:
https://weather.us/forecast/2643743-london/ensemble/euro/temperature
The operational run has a clear zonal "sine wave" effect, flitting between very warm and cool conditions at 850. (The same "sine wave" effect is visible in the mean, albeit to a much lower degree).
The T2Ms, however, differ far less, ranging from 21 to 24 - the average to rather warm conditions that I've been going on about for the best part of a week.
That doesn't preclude the odd warm or even very warm day, but of note is the fact that even the 90th percentile only reaches 26C.
I wouldn't rule out the chance of an odd 27 or 28, even, but that would be the exception rather than the rule.
Like it or not, the pattern has changed away from our blocking high and heat-hounds will need to make the most of any brief ridges that pop up.