Moscow has a humid continental climate (Köppen climate classification Dfb) with warm, sometimes hot, somewhat humid summers and long, cold winters. Typical high temperatures in the warm months of June, July and August are around 23 °C (73 °F), but during heat waves, which can occur anytime from May to September, daytime temperature highs often top 30 °C (86 °F) for sometimes one or two weeks. In the winter, temperatures normally drop to approximately −10 °C (14 °F), though there can be periods of warmth with temperatures rising above 0 °C (32 °F). Summer lasts from mid-May to the beginning of September.