The season which contains temperatures tolerable for being on the water is quite long. Usually from April-ish until November and sometimes December.
The season which contains good sailing can be a bit less. It depends on how long the Bermuda high pressure systems hang around, killing the breeze during the summer. Also, some people regard summer as too hot to enjoy.
I object to the idea that the wind on the Chesapeake can be grouped into "seasons". The wind here is fickle, unreliable, and knows exactly how to vary in strength and direction to maximize frustration and anxiety. Take, for example, yesterday:
7:00 AM - Chestertown - the tide has turned in my favor. There's a light breeze from the S/SW, which is where I need to go, so I motor downriver for a mile or so, past "Devil's Reach" (so named because it was hard to tack through in days of yore).
8:00 - 11:00 or so - tacking against wind that fluctuates up to 60 degrees especially just as I try to round each bend in the river. This takes so long that the current is now against me.
12:00 - I finally reach the open part of the river, and now the wind's blowing 15 knots plus from the SW. I change jibs and tack W and S against this for the next few hours. There are some sailboat races going on, with a few cruiser types motoring around them.
2:00 - I reach the part where a SW wind would be perfect to get around the bend in the river, something I've been waiting for, and the wind dies. I motor to the green can at the bend and put up the 135 genoa. While motoring, the breeze seems to pick up and I get the impression that the next leg will be great.
3:00 - 4:30 - It turns out the breeze I felt was all in my head, and there's not even enough breeze to sail a deep reach effectively, though this would have been a sled ride if the wind that I had to tack against for so long had held.
4:30-5:00 - I round Love Point and reach the open bay. There are warnings of thunderstorms on the radio and I can see a large one over the land to the west. The wind is now blowing 20 knots from the south, the direction of the bay bridge. I take down the 135 and once again put up my ancient reefed jib and tack toward the bridge as the seas and wind build. Luckily the thunderstorm dissipates, but there's much anxiety about going under the bridge when I can only tack parallel to it. I worry that the boat will stall when hit by a wave and what it will say in the newspaper about me when I smash the boat into an abutment. Cargo ships and barges pick just the moment I get close to the bridge to appear out of nowhere. I nearly get run over by a motor boat bashing and pitching through the waves on its way to the yacht club on the eastern end of the bridge.
6:30 - We finally make it under the bridge. Heeling 30 degrees and bashing through seas large enough to drench me and the boat. A few come aboard into the cockpit. I'm soaked.
7:30 - When I reach the yellow A marker off of Annapolis, I turn up the river. 1 mile later, even with the Naval Academy, I could be on a lake - some following wind, but no sign at all of the conditions I just left.
7:30 - 10:00 or so - I glide 8 miles up the river to the dock with a steady but barely noticeable tail wind .