Most of Indiana has a humid continental climate (Koppen climate classification Dfa), with hot, humid summers and cool to cold winters. The extreme southern portions of the state border on a humid subtropical climate (Koppen Cfa) with somewhat milder winters. Summertime maximum temperatures average around 85 °F (29 °C) with cooler nights around 60 °F (16 °C). Winters are a little more variable, but generally cool to cold temperatures with all but the northern part of the state averaging above freezing for the maximum January temperature, and the minimum temperature below 20 °F (-8 °C) for most of the state. The state receives a good amount of precipitation, 40 inches (1,000 mm) annually statewide, in all four seasons, with March through August being slightly wetter.

The state does have its share of severe weather, both winter storms and thunderstorms. While generally not receiving as much snow as some states farther north, the state does have occasional blizzards, some due to lake effect snow. Two major paralyzing snowstorms bear merit. The January, 1978 Blizzard, which affected almost the entire state, and the December, 2004 Blizzard, which primarily affected the Ohio Valley and later caused the severe flooding of the White, Wabash, and the Ohio Rivers in January, 2005. The state averages around 40-50 days of thunderstorms per year, with March and April being the period of most severe storms. While not considered part of Tornado Alley, Indiana is the Great Lakes state which is most vulnerable to tornadic activity. In fact, three of the most severe tornado outbreaks in U.S. history affected Indiana, the Tri-State Tornado of 1925, the Palm Sunday tornado outbreak of 1965 and the Super Outbreak of 1974. The Evansville Tornado of November 2005 killed 25 people, 20 people in Vanderburgh County and 5 in Warrick County.