Flagstaff has a rather dry semi-continental climate (Köppen Dsb/Csb).[22] Flagstaff has five distinct seasons: a cold and snowy winter, with extended dry periods punctuated with deep snows about once every 3-4 weeks; a dry and windy spring with occasional snows; a very dry and hot early summer from May to early July; a wet and humid monsoon season from July to early September; and a dry and pleasant fall which lasts until the first snows in November.
The combination of high elevation and low humidity provide mild weather conditions throughout most of the year. The predominantly clear air and high elevation radiates daytime heating effectively resulting in overnight temperatures generally much lower than the daytime temperature. This means a 55 degree day in January can drop to 15 at night. Winter nights in fact can be very cold, with temperatures sometimes dropping far below zero.[23]
Winter weather patterns in Flagstaff are cyclonic and frontal in nature, originating in the eastern Pacific Ocean. These deliver periodic, widespread snowfall followed by extended periods of fair weather. The area's generally stable weather pattern is broken by brief, but often intense, afternoon downpours and dramatic thunderstorms common during the monsoon of July and August. Summer temperatures are moderate and high temperatures average around 82 °F (27.8 °C).[8] Extreme temperatures range from −30 °F (−34 °C) on January 22, 1937, and up to 97 °F (36 °C) on July 5, 1973, respectively.[24] The weather in Flagstaff is generally sunny. In fact Flagstaff gets more sunshine than snow cities such as New York City, Chicago, Boston and Denver. Flagstaff is only the only city in Arizona to have not reported temperatures of 100 °F (38 °C) or higher.[24]
The annual snowfall averages 100.3 inches (255 cm), placing Flagstaff among the snowiest incorporated cities in the United States.[25] Overall, the city features an average of 276 days without measurable precipitation each year. Despite snow storms often being spread weeks apart, snow often covers the ground for weeks after major winter storms due to the low night temperatures refreezing the snowpack, even when daytime temperatures are above freezing. However, due to the infrequent and scattered nature of the snowstorms, persistent snow pack into spring is rare.[8] One notable exception occurred during the severe winter of 191516, when successive Pacific storms buried the city under over 70 inches (178 cm) of snow, and some residents were snowbound in their homes for several days