Located in the northeastern reaches of the Sonoran Desert, Phoenix has a subtropical arid climate with hot summers and warm winters. On average, Phoenix has only 5 days per year where the temperature drops to or below freezing. Phoenix averages 85% of sunny days and receives very little rainfall, the average annual total at Phoenix Sky Harbor International Airport being 8.3 inches. Although thunderstorms are possible at any time of the year, they are most common during the monsoon from July to mid-September as humid air surges in from the Gulf of California. Winter storms moving inland from the Pacific Ocean occasionally produce significant rains but occur infrequently.