Casper, as with most of the rest of Wyoming, has a semi-arid climate (Köppen climate classification BSk), with long, cold, but dry winters, hot but generally dry summers, mild springs, and short and crisp autumns. Highs range from 32 °F (0 °C) in January to 88 °F (31.1 °C) in July and August. Temperatures typically plummet during summer nights, with an average diurnal temperature range approaching 35 °F (19.4 °C). Snow can fall heavily during the winter months, being the greatest in April, and usually falls in May and October, but rarely September. Precipitation is greatest in spring and early summer, but even then it is not high. Highs reach 90 °F (32.2 °C) on 31 days per year and fail to surpass freezing on 46. Lows drop to 0 °F (−17.8 °C) on 18 nights per winter
