Spokane has a dry summer continental climate , a rare climate due to its elevation and significant winter precipitation; Spokane, however, is adjacent to and sometimes even classified as a warm-summer Mediterranean climate (Csb) because the average temperature for the coldest month is just over 26.6 °F (−3 °C).
The area typically has a hot, arid climate during the summer months, bracketed by short spring and fall seasons. On average, July and August are equally warm, and the coolest month is December; July averages 69.5 °F (20.8 °C), while December averages 27.5 °F (−2.5 °C). Daily temperature ranges are large during the summer, often exceeding 30 °F (17 °C), and small during the winter, with a range just above 10 °F (5.6 °C). The record high and low are 108 °F (42 °C) and −30 °F (−34 °C), but temperatures of more than 100 °F (38 °C) or less than −10 °F (−23 °C) are rare. Temperatures above 90 °F (32 °C) occur an average of 19 days annually, temperatures above 100 °F (38 °C) occur an average of only 1 day annually, and those below 0 °F (−18 °C) average 3.5 days a year.
Spokane’s location, between the Cascades Range to the west and the Rocky Mountains to the east and north, protects it from weather patterns experienced in other parts of the Pacific Northwest. The Cascade Mountains form a barrier to the eastward flow of moist and relatively mild air from the Pacific Ocean in winter and cool air in summer. As a result of the rain shadow effect of the Cascades, the Spokane area has 16.5 inches (420 mm) average annual precipitation, less than half of Seattle’s 37 inches (940 mm). Precipitation peaks in December, and summer is the driest time of the year. The Rockies shield Spokane from some of the winter season’s coldest air masses traveling southward across Canada.