Indiana State Climate
Indiana, like most Midwestern states, has a humid continental climate that is distinguished by cool, sometimes bitterly cold, winters and warm to hot, humid summers with abundant rainfall. The state’s year-round average of 3 to 4 inches (76–102 mm) of rain per month, falling on some of the country’s richest topsoil, has allowed it to become one of the most productive farmlands on earth.
In its extreme south, bordering the Ohio River, Indiana shifts to a humid subtropical climate that is much like humid continental, but with milder winters and somewhat greater rainfall.
Because it has no high natural barriers to protect it from warm, moist southern winds or cold, dry northern air masses, weather in Indiana is often dramatic, marked by tornadoes in spring, thunderstorms in summer, and blizzards in winter. Flooding is sometimes a problem in the state’s more heavily watered south. When they occur, droughts tend to be in the south.
Annual snowfall averages less than 22 inches (560 mm), very low compared to neighboring Midwestern and Northeastern states. The heaviest snow tends to fall in the north, especially near Lake Michigan where "lake-effect" storms—generated by cold winds picking up abundant moisture off a warm body of water—can create heavy snowfalls and blizzards.
Winters in Indiana are cold, sometimes bitterly so. Average temperatures increase moving south. While Lake Michigan moderates temperatures in the extreme northwest, it can also produce heavy lake-effect snowfalls and blizzards.
In spring, Indiana temporarily becomes the most tornado-prone state in the country—a distinction it yields as summer nears. Rainfall totals make this and summer the two wettest seasons.
Summers in Indiana are warm to hot and usually humid. The weather is warmest toward the state’s southern part. Thunderstorms are common, and this is the season of heaviest, most evenly distributed rainfall.
Autumn high temperatures range from the high 70s F (25–26°C) in September to the mid 60s F (18–19°C) in October, cooling down to the low 50s F (11–12°C) by November. September and October’s lingering warmth often produces a classic "Indian summer" that mixes warm days and cool evenings to accompany the annual fall change of foliage colors. This season has the second lowest average rainfall.
Indiana’s annual mean temperature depends on location. It’s 49–58°F (9–12°C) in the north and 57°F (14°C) in the south. Summers can be hot, although more as a result of humidity than temperatures. Daytime highs average 88°F (31°C) in July, with occasional readings in the 90s F (32–37°C). While winter temperatures occasionally can fall below 0°F (-18°C), January readings more typically range from 17°F (-8°C) to 35°F (2°C), with warmer temperatures occurring further south.
At 152°F (84.4°C), Indiana is in the middle tier of states that have the greatest extremes between their all-time high and low temperatures, ranking 28th. Its all-time high of 116°F (46.7°C) was set on July 14, 1936, at Collegeville, 90 miles northwest of Indianapolis. The all-time coldest temperature of -36°F (-37.8°C) was set on January 19, 1994, at New Whiteland, a small town about 10 miles due south of Indianapolis.
With an annual statewide average rainfall of 41.72 inches (1,060 mm), Indiana is the 26th wettest state in the United States. The state’s driest location is Monroeville, in northeast Indiana, which receives 33.74 inches (857 mm) of rain per year. English, in southern Indiana, is the state’s wettest locale, receiving 49.72 inches (1,263 mm) of rain annually.
Among major cities, Evansville, in the extreme southwest, receives 44.27 inches (1,124 mm) of rain per year, while South Bend, in the extreme north, receives 39.7 inches (1,008 mm). The slight difference between the two cities is indicative of the rather uniform rainfall pattern over the state. The state record for rainfall in one year, 97.38 inches (2,473 mm/8.12 feet), was set in 1890 in Marengo, a small town in the south about 30 miles west of Louisville, Kentucky.
Rain falls fairly evenly through the year. Spring and summer are the wettest seasons, with an average of 4 inches (102 mm) falling each month from April through August. Autumn is the next wettest season, averaging about 3 inches (76 mm) per month, while winter months average about 2.5 inches (64 mm) per month.
In contrast to their similar rainfall figures, Evansville and South Bend have widely different annual snowfall figures: 14.1 inches (358 mm) for the former and 69.9 inches (1,775 mm/5.83 feet) for the latter. In between those extremes, Fort Wayne, on the eastern border with Ohio, receives 33 inches (838 mm) of snowfall annually while Indianapolis, in the state’s geographic center, receives 23.9 inches (607 mm). The one-season snowfall record is 172 inches (4,369 mm/feet), set in 1977–78 at South Bend.
With its humid continental climate, the state’s cities have high relative humidities that match surrounding states and even some parts of the Deep South. Comfort or discomfort from high humidity in such a climate is related to temperature. (A high relative humidity reading does not create discomfort if it is accompanied by a moderate temperature.)
There is a higher percentage of sunshine hours moving east and south across the state. Centrally located Indianapolis receives 40 percent of all available sunshine hours in January, compared to 42 percent for Evansville in the south and 46 percent for Fort Wayne in the east. In July, the same pattern applies: Indianapolis receives 66 percent of all available sunshine hours, while Evansville and Fort Wayne receive 73 percent and 75 percent, respectively.
Evansville in the south enjoys 27 more clear days than South Bend in the north, but has exactly the same number of partly cloudy days. The difference is that the southern city, in a slightly warmer and sunnier climate, has 27 fewer cloudy days per year.
While the state has three distinct geographical regions, climatically it divides into two equal-sized regions: a wetter, warmer southern half and a somewhat drier, colder northern half. There is a small area in the state’s northeast where rainfall is somewhat lower than the two other regions.
Indiana receives an average of 20 tornadoes per year, the third most per year per 10,000 square miles (16,093 sq km). In 1965, 137 people died as a result of tornadoes, and in 1974, 47 people died. Since then, the most people the state has lost to a tornado in one year has been eight.
Lake Michigan is also a source of blizzards created by lake-effect snowstorms. Despite the usually moderating influence of the lake, Indiana’s northwest corner at times can have the state’s heaviest snowfall.
Floods, as well as droughts, tend to occur most heavily in the south near the Ohio River. The south’s hilly terrain encourages faster run-off, which in heavy rains can cause flood conditions.
Thunderstorms occur mostly in summer. Thunderstorm days in the state average between 30 and 50 per year.
-World Trade Press