Be respectful
Is the red line the average, and the green line the difference?
Green line is the average temperature for that day this year.
Red line is the average temperature for that day for 30 years, 1991-2020.
In the chart, the red areas are days hotter than average and blue areas lower than average.
There is also daily precipitation as bar charts on the bottom. It's a shame those don't have daily averages for 30 years though.
Whats the grey area?
I think it's the difference between the highest and lowest temperatures that day across the 30 year range.