I switch to winters when the forecast is for temperatures to routinely be below freezing overnight. I'll risk a random frost night if the temps go back above freezing during the day.
Same for switching back to summers. The forecast needs to be routinely above freezing on the overnight temps.
Sadly, here in Minnesota, that usually means winters on the end of October, and not off until the end of April. Worse this year.
Even without snow, driving summers in the cold is not wise.