Was originally curious about summer specific horror movies but realized there was no reason to limit the discussion. For my example I have yet to see a movie that even comes close to Midsommar in terms of summer-y vibes.
Two that I just watched that felt pretty summer-y: X and Pearl.
And some others that are not necessarily the best, but are on fall and winter movie lists of mine:
Fall: Sleepy Hollow, Jeppers Creepers, An American Werewolf in London, Candyman, Fright Night
Winter: Snowpiercer, Gremlins, The Wolf of Snow Hollow, The Thing, Black Christmas
Can’t believe I forgot the other quintessential summer horror movie: Texas Chainsaw Massacre
I spent July 4 rewatching I Know What You Did Last Summer. It just seemed appropriate. Wish I’d thought about Midsommar. That’s a great movie.
Summer: I guess anything that takes place at camp: Friday the 13th, The Burning, Sleepaway Camp, etc.
Fall: Halloween, obviously.
Winter: The Shining. More recently I liked The Lodge. Frozen was good too.
Spring: Hmm…not sure about this. April Fool’s Day is the first movie off the top of my head that definitely takes place in spring. What else signifies spring? Easter? Spring Break?