Here in the verdant spring of Maryland, we have cool nights. 

I have a cheap acrylic guayabera, split down one side from use.. I wear it out on the back deck in the blessedly chilly May spring nights here. 

Frederick lies in the lap of the Catoctins by the Appalachian trail, so remnants of mountain weather wash down to us. I was up on the mountains at Gambrill State Park a week or so ago, checking out nonexistent morels. The mist was so bad that I kept wanting to clean my glasses: I don't wear any. The wind was so bad, I could lean on it when hiking uphill. 

I remember May as the worst time of year, in Texas, when there was no longer any hope of cool breezes, and the humidity really started to kick in. Hope just dies in that kind of heat. Hope, energy and optimism simply wither in the hothouse heat. 

We've had to run the cool side of the heat pump, once. 

It's the only side that seems to work..