Indianapolis has a humid continental climate , but can be considered a borderline humid subtropical climate using the −3 °C (27 °F) isotherm. It experiences four distinct seasons. The city is in USDA hardiness zone 6a.
Typically, summers are hot, humid and wet. Winters are generally cold with moderate snowfall. The July daily average temperature is 75.4 °F (24.1 °C). High temperatures reach or exceed 90 °F (32 °C) an average of 18 days each year, and occasionally exceed 95 °F (35 °C). Spring and autumn are usually pleasant, if at times unpredictable; midday temperature drops exceeding 30 °F or 17 °C are common during March and April, and instances of very warm days (80 °F or 27 °C) followed within 36 hours by snowfall are not unusual during these months. Winters are cold, with an average January temperature of 28.1 °F (−2.2 °C). Temperatures dip to 0 °F (−18 °C) or below an average of 4.7 nights per year.
The rainiest months occur in the spring and summer, with slightly higher averages during May, June, and July. May is typically the wettest, with an average of 5.05 inches (12.8 cm) of precipitation. Most rain is derived from thunderstorm activity; there is no distinct dry season, although occasional droughts occur. Severe weather is not uncommon, particularly in the spring and summer months; the city experiences an average of 20 thunderstorm days annually.
The city’s average annual precipitation is 42.4 inches (108 cm), with snowfall averaging 25.9 inches (66 cm) per season. Official temperature extremes range from 106 °F (41 °C), set on July 14, 1936, to −27 °F (−33 °C), set on January 19, 1994.