In Cairo, and along the Nile River Valley, the climate is a hot desert climate (''BWh'' according to the Köppen climate classification system). Wind storms can be frequent, bringing Saharan dust into the city, from March to May and the air often becomes uncomfortably dry. High temperatures in winter range from , while night-time lows drop to below , often to . In summer, the highs rarely surpass , and lows drop to about . Rainfall is sparse and only happens in the colder months, but sudden showers can cause severe flooding. The summer months have high humidity due to its coastal location. Snowfall is extremely rare; a small amount of graupel, widely believed to be snow, fell on Cairo's easternmost suburbs on 13 December 2013, the first time Cairo's area received this kind of precipitation in many decades. Dew points in the hottest months range from  in June to  in August.