Roland Barthes wrote in his mythologies that the writer is never really on vacation; because he spends his time writing wherever he wants to go. Being more relaxed in the summer (in terms of activities and not government news) frees the brain to wander and that is how good, persistent ideas appear.
It is probably a myth that the heat does not allow us to concentrate as much as the winter. A good antidote for the heatwave could be, precisely, to start reading Russian writers, always overwhelmed by the snowfall.