to be fair, I think it's more likely to get such a departure from average in the summer if you have a renegade closed off low and onshore flow with rain. Average temperatures mute the extremes, so they don't really show us extreme highs or extreme lows.
As an example July 1993 which had our most extensive and extreme heatwave of my adult lifetime (July 1977 had an even more extreme one but I was only 3 years old lol), had a day with a high of 66 and a low of 62 on the 2nd, because of a big rainstorm with onshore flow and high winds. A week later the historic heatwave started.