Greece does not get dew very often because the daytime/nighttime temperatures do not vary very much. The average dew point is 1 degree celsius and the temperature does not get low enough.
Santorini's most common rainfall types are light rain, thundersorms and moderate rain. Thunderstorms occur mostly in the warm season and light rain in the cold season.
During the warm season they experience many high pressure systems keeping the skies clear and during the cold seasons they have low pressure meaning they have cloud coverage.
Because Santorini is near the equator is is warm. It is on the coast so temperatures stay mild. Ocean currents bring cloud in mostly in winter. It is moderatly windy year round. The are no mountain barriers and is flat it has a low altitude. High pressure belts keep the skies clear in summer.