You don't necessarily have to wait for bad weather to hit. I was in Boston in February and had a Monday flight BOS-DFW-NRT-BKK. On Saturday the forecast for Monday (and Tuesday) was snow, snow and more snow, starting around noon. Called AA and asked if I could fly to DFW on the first flight out on Sunday. No prob, no charge. I'm sure that they were probably thrilled to have one fewer pax who might have been affected by yet another snowstorm in Boston.