Sunday was grey when we went to 'Chuck's Beach'. (our friend Chuck has named different beaches after himself and his grandchildren. These are accessible via dune paths.)
Wednesday was sunny and gorgeous when we went to 'Crab Beach'. (given it's name by Chuck due to the amount of Fiddle crabs on the inlet.)
Both days were awesome and because we're on Nantucket, every day is a beautiful day no matter the weather.