Boulder has a rather dry climate typical of much of the state, and receives many sunny or mostly sunny days each year. Under the Köppen climate classification, central parts of the city have a semi-arid climate (Köppen BSk). Winters are cool to occasionally bitterly cold, with highs averaging in the mid to upper 40s °F (7–9 °C). Lows may plummet below −10 °F (−23 °C) on a few nights per year, but extended subzero cold is uncommon. Because of orographic lift, the mountains to the west often dry out the air passing over the Front Range, often shielding the city from precipitation in winter, though heavy falls may occur. Snowfall averages 85 inches (220 cm) per season, but snow depth is usually shallow; a strong warming sun due to the high elevation can quickly melt snow cover during the day. Occasionally, Chinook winds bring rapid warm-ups. Summers are hot and dry, with 27 days reaching 90 °F (32 °C) or above. Nights are significantly cooler than days year-round due to the high-elevation dry climate
