Boulder has a dry climate. (Much of Colorado is dry.) It has many sunny or mostly sunny days every year. According to the Köppen climate classification, the city's climate is "semi-arid" (Köppen "BSk"). Winters are cool, but sometimes can get very cold. During the winter, the high temperature is usually in the mid- to upper- 40s°F (7–9 °C). The low temperature in winter can be below −10 °F (−23 °C) on a few nights. Usually it does not stay below 0 °F (−18 °C) for many days at a time. 