When the weatherman announces a heat wave or an upcoming drought, put away your mower for the moment. Longer grass will shade the soil, keeping it cooler, and this will help protect the grass roots. Mowing short is even worse: the lawn’s roots can be damaged if the sun’s rays strike them directly, which is what happens when you scalp a lawn.
And besides, who wants to mow when temperatures soar to 85? F (30? C) and above?
Take up mowing again only with the return of cooler temperatures.