As the macros scale drivers of weather change across as the seasons I can see why you could get months being outliers for years on end. That plus of course random chance.
If there’s a large scale SST pattern that favours high pressure over us in June and low pressure in August, and that pattern has interannual persistence, then you could get a string of sunny Junes and cloudy Augusts. An example often quoted is El Niño favouring blocked conditions in late winter but not early winter. So a decade with lots of El Ninos might see a tendency to cold February and March, but mild Dec and Jan.
In the early summer months I understand the big shifts include:
- Melting of Eurasian snow
- Onset of the Summer monsoon circulation
- Northward shift of the subtropical jet and Hadley cell over the Med
That is all connected to some extent and partly accounts for switches in July
In late summer and early Autumn we then have:
- Reversal of temperature difference between Atlantic SST and land heating
- Onset of Atlantic hurricane season
This potentially explaining the fact weather often shifts around the August bank holiday.
These shifts, particularly the SST gap, I think also account for the fact Western oceanic areas are generally better in Spring and early summer while Eastern more continental counties do relatively better in late summer.
Brockley, South East London 30m asl