There are certain days throughout the year that signify the official start of the seasons. And they can be different for everyone (though some are pretty standard).
For example, the turning of the leaves in Autumn, the first snow in Winter, and the first sight of a Robin in Spring.
But for me, the official start of the summer is that first day you can drive home from work with the window rolled all the way down. Arm resting on the door. And that day was Thursday. Since then I have spent the last three days walking Leia in nothing but shorts and a t-shirt. The feeling is wonderful.
What kicks off your summer? The first whiff of someone's grill? The first echo of a far off lawn mower? The first trip to the beach? What?