Late August can bring thunderstorms. When I rode the GAP as part of a cross-PA trip starting the Saturday after Labor Day is rained for a few days before my arrival in PGH that Friday, but the trail was pretty much dry by Saturday. Saturday was pretty warm and sticky, with a moderate headwind in places. Later in the trip, near New Berlin, PA, a massive thunderstorm moved in from the south while I was in camp. Sheets of wind-swept rain for at least 35 minutes. Thought I would emerge from the laundry building to find my tent blown into the pond it was pitched near.