This is a really super visualisation. Great work.

I have one quick question about the data, which was inspired by the little maps showing the regional differences. I hope you don't mind me asking because I can't find a clear answer by Googling it.

Are the national average figures weighted by population or by area?

I expect it's probably by area. Unfortunately, since England has about 80% of the UK's population in about 50% of the area, this can lead to situations where the national average picture (as in your line charts) is not consistent with what most people actually experience. The sunshine in July would seem to be an example of this, where the line chart suggests "about average" but the map shows that most people would have experienced "well above average".