Climate of Illinois
Encyclopedia
Because of its nearly 400 miles (643.7 km) length and mid-continental placement, Illinois
Illinois
Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...
has a widely varying climate. Most of Illinois has a humid continental climate
Humid continental climate
A humid continental climate is a climatic region typified by large seasonal temperature differences, with warm to hot summers and cold winters....
(Koppen climate classification
Köppen climate classification
The Köppen climate classification is one of the most widely used climate classification systems. It was first published by Crimea German climatologist Wladimir Köppen in 1884, with several later modifications by Köppen himself, notably in 1918 and 1936...
Dfa) with hot, humid summers and cool to cold winters. The southernmost part of the state, from about Carbondale
Carbondale, Illinois
Carbondale is a city in Jackson County, in the state of Illinois, within the Southern Illinois region. It is located at the junction of Illinois Route 13 and U.S. Route 51, southeast of St. Louis, Missouri, on the northern edge of the Shawnee National Forest...
southward, borders on a humid subtropical climate
Humid subtropical climate
A humid subtropical climate is a climate zone characterized by hot, humid summers and mild to cool winters...
(Koppen Cfa) with more moderate winters. Average yearly precipitation for Illinois varies from just over 48 inches (1,219.2 mm) at the southern tip to 35 inches (889 mm) in the northern portion of the state. Normal annual snowfall exceeds 38 inches (965.2 mm) in Chicago
Chicago
Chicago is the largest city in the US state of Illinois. With nearly 2.7 million residents, it is the most populous city in the Midwestern United States and the third most populous in the US, after New York City and Los Angeles...
, while the southern portion of the state normally receives less than 14 inches (355.6 mm). The highest temperature recorded in Illinois was 117 °F (47 °C), recorded on July 14, 1954, at East St. Louis, while the lowest temperature was -37 °F (-39 °C), recorded on January 15, 2009, at Rochelle
Rochelle, Illinois
Rochelle is a city in Ogle County, Illinois, United States. The population was 9,574 at the 2010 census, up from 9,424 at the 2000 census. Rochelle is about west of Chicago and south of Rockford...
.
Illinois averages around 50 days of thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
activity a year which put it somewhat above average for number of thunderstorm days for the United States. Illinois is vulnerable to tornadoes with an average of 35 occurring annually, which puts much of the state at around 5 tornadoes per 10000 square miles (25,899.9 km²) annually. The deadliest tornado on record in the nation occurred largely in Illinois. The Tri-State Tornado
Tri-State Tornado
The Tri-State Tornado of Wednesday, March 18, 1925, was the deadliest tornado in U.S. history. With 695 confirmed fatalities, the tornado killed more than twice as many as the second deadliest, the 1840 Great Natchez Tornado...
of 1925 killed 695 people in three states; 613 of the victims lived in Illinois.
Temperatures
Due to the urban heat islandUrban heat island
An urban heat island is a metropolitan area which is significantly warmer than its surrounding rural areas. The phenomenon was first investigated and described by Luke Howard in the 1810s, although he was not the one to name the phenomenon. The temperature difference usually is larger at night...
effect, cities tend to be 2 °F (1 °C) warmer on average, which is most noticeable overnight.
Heat
The highest temperature recorded in Illinois was 117 °F (47.2 °C), recorded on July 14, 1954, at East St. Louis. The 1995 Chicago heat wave1995 Chicago heat wave
The 1995 Chicago heat wave was a heat wave which led to approximately 750 heat-related deaths in Chicago over a period of five days. Eric Klinenberg, author of the 2002 book Heat Wave: A Social Autopsy of Disaster in Chicago, has noted that in the United States, the loss of human life in hot spells...
was one of the worst weather-related disasters in state history, with 525 dead within a five day period as overnight lows rose as high as 84 °F (28.9 °C) and daytime highs rose to 106 °F (41.1 °C). The most deadly heatwave in the history of the United States struck Illinois during July 1936, which killed 2656 people.
Cold
Extreme temperatures changes can occur within minutes with the passage of a strong cold frontCold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
through the state. On December 20, 1836, temperatures fell 40 degrees Fahrenheit in minutes, which supposedly froze people to their saddles and chickens in their tracks. The lowest temperature was -37 F, recorded on January 15, 2009, at Rochelle
Rochelle, Illinois
Rochelle is a city in Ogle County, Illinois, United States. The population was 9,574 at the 2010 census, up from 9,424 at the 2000 census. Rochelle is about west of Chicago and south of Rockford...
.. However, the official record-lowest temperature for the state is -36 degrees Fahrenheit, recorded at Congerville
Congerville, Illinois
Congerville is a village in Woodford County, Illinois, United States. The population was 466 as of the 2000 census. Congerville is part of the Peoria, Illinois Metropolitan Statistical Area.-State Record:...
on 5 January 1999..Prolonged cold struck the upper Midwest between January 30 and February 5, 1996, as low temperatures during the period averaged -25 F across the northwest corner of the state.
Averages
| City | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cairo | 41/25 | 47/29 | 57/39 | 69/50 | 77/58 | 86/67 | 90/71 | 88/69 | 81/61 | 71/49 | 57/39 | 46/30 |
| Chicago | 31/16 | 35/20 | 47/29 | 59/39 | 70/48 | 80/58 | 84/64 | 82/63 | 75/54 | 62/43 | 48/32 | 35/21 |
| Edwardsville | 36/19 | 42/24 | 52/34 | 64/45 | 75/55 | 84/64 | 89/69 | 86/66 | 79/58 | 68/46 | 53/35 | 41/25 |
| Moline | 30/12 | 36/18 | 48/29 | 62/39 | 73/50 | 83/60 | 86/64 | 84/62 | 76/53 | 64/42 | 48/30 | 34/18 |
| Peoria | 31/14 | 37/20 | 49/30 | 62/40 | 73/51 | 82/60 | 86/65 | 84/63 | 77/54 | 64/42 | 49/31 | 36/20 |
| Rockford | 29/13 | 34/17 | 46/27 | 60/38 | 71/48 | 81/58 | 84/63 | 82/61 | 75/52 | 62/40 | 47/30 | 33/17 |
| Springfield | 33/17 | 39/22 | 51/32 | 63/42 | 74/53 | 83/62 | 86/66 | 84/64 | 78/55 | 67/44 | 51/34 | 38/23 |
Precipitation
Average yearly precipitation for Illinois varies from just over 48 inches (1,219.2 mm) at the southern tip to just under 32 inches (812.8 mm) in the northern portion of the state. May and June are the wettest months of the year. Flooding is the most damaging weather hazard within the state. Increased warming within urban heat islands leads to an increase in rainfall downwind of cities. Lake MichiganLake Michigan
Lake Michigan is one of the five Great Lakes of North America and the only one located entirely within the United States. It is the second largest of the Great Lakes by volume and the third largest by surface area, after Lake Superior and Lake Huron...
leads to an increase in winter precipitation along its south shore due to lake effect snow
Lake effect snow
Lake-effect snow is produced during cooler atmospheric conditions when cold winds move across long expanses of warmer lake water, providing energy and picking up water vapor which freezes and is deposited on the leeward shores...
forming over the relatively warm lakes. In summer, the relatively cooler lake leads to a more stable atmosphere near the lake shore, reducing rainfall potential.
Snowstorms
While normal annual snowfall exceeds 38 inches (965.2 mm) in Chicago, and the southern portion of the state normally receives less than 14 inches (355.6 mm), The snowiest winter on record for Chicago was 89.7 inches (227.8 cm) during the winter of 1978/1979. During the winter of 1830/1831, southern sections of the state were covered with 3 foot (0.9144 m) of snow, with drifts up to 6 feet (1.8 m) tall. Storms exceeding the normal winter value are possible within one day. The heaviest snowfall recorded in recent history for Chicago was 23 inches (584.2 mm) in 10 hours during January 26, 1967.Thunderstorms and severe weather
Illinois averages around 50 days of thunderstormThunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
activity a year which put it somewhat above average for number of thunderstorm days for the United States. Thunderstorms contribute over half of the annual precipitation statewide. Illinois is vulnerable to tornadoes with an average of 35 occurring annually, which puts much of the state at around 5 tornadoes per 10000 square miles (25,899.9 km²) annually. Peak tornado activity occurs between April and June. The deadliest tornado on record in the nation occurred largely in Illinois. The Tri-State Tornado
Tri-State Tornado
The Tri-State Tornado of Wednesday, March 18, 1925, was the deadliest tornado in U.S. history. With 695 confirmed fatalities, the tornado killed more than twice as many as the second deadliest, the 1840 Great Natchez Tornado...
of 1925 killed 695 people in three states; 613 of the victims lived in Illinois. Illinois also receives the remnants of tropical cyclone
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
s which have struck the Gulf coast. One of the wetter systems, Tropical Storm Claudette
Tropical Storm Claudette (1979)
Tropical Storm Claudette was a long living tropical storm that produced heavy rain across Puerto Rico and Texas in late July 1979. The storm killed 2 people and left $1.1 billion in damage...
, impacted the state in July 1979 bringing rainfall amounts up to 7.64 inches (194.1 mm).
See also
- Cold waveCold waveA cold wave is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in temperature within a 24 hour period requiring substantially increased protection to agriculture, industry, commerce, and...
- Heat waveHeat waveA heat wave is a prolonged period of excessively hot weather, which may be accompanied by high humidity. There is no universal definition of a heat wave; the term is relative to the usual weather in the area...
- List of wettest known tropical cyclone remnants in Illinois