This summer's heat wave could have been caused by a huge volcanic eruption.
https://www.nasa.gov/feature/jpl/tonga-eruption-blasted-unprecedented-amount-of-water-into-stratosphere
What is important is not the general weather but the weather on Test days.
Someone has counted up the number of days washed out in Tests up to 2004.
https://community.netweather.tv/topic/16950-number-of-days-washed-out-for-test-matches-in-engl/
Old Trafford: 29 days washed out.
Headingley: 12 days washed out.
Pretty conclusive though someone might like to do further research to see if the same trend continued after 2004.