That's a great point about traffic peaking for certain outdoor activities at certain times. I wonder if we could borrow an idea from the SciFi.SE site. Over at https://scifi.stackexchange.com/ they do weekly themes and have prizes for top questions and such. Not saying we need to have prizes right away, but making a push for themed questions in the correct seasons could help spur seasonal traffic.
Summer: Canoeing, Fishing
Fall: Hiking, Backpacking
Winter: Skiing, ice-fishing
Spring: Bird-watching, Thru-hike
So then each of those would be a tag that users would add to their question during the week/month of the competition. Not really sure where we go from there because I don't know what is reasonable. A partnership with an outdoor company and some SWAG would be awesome.