Yarmouth is primarily a summer destination. June through August is peak season — the beaches are busy, the restaurants are all open, and the Route 6A antique shops are stocked. July and August are the most crowded; late June and September are ideal if you want good weather without the full summer crowds.
Autumn is lovely: the traffic disappears, the foliage along Route 6A turns brilliant in October, and many of the cultural venues stay open into fall. Winter on the Cape is quiet — most seasonal businesses close after Columbus Day, though some year-round restaurants and shops remain. The Edward Gorey House has limited winter hours; check ahead.
Spring arrives gradually; May is pleasant but unreliable weather-wise, and the water is too cold for swimming until late June.