Longer days

I'm appreciating the longer hours of daylight. Indeed, though spring seems to have barely arrived, we are less than a month away now from summer solstice. But real summer weather starts after that. It's a variation on "When the days begin to lengthen, the cold begins to strengthen," going in the other direction. "When the days begin to shorten . . ." That doesn't work. "When the light starts decreasing, the temperatures start increasing"?