Climate of Illinois

Due to the urban heat island effect, cities tend to be {{convert|2|°F-change|°C-change|1|disp=or}} warmer on average, which is most noticeable overnight.Illinois State Water Survey. [http://www.sws.uiuc.edu/atmos/statecli/General/Illinois-climate-narrative.pdf Climate of Illinois.] {{Webarchive|url=https://web.archive.org/web/20080625044726/http://www.sws.uiuc.edu/atmos/statecli/General/Illinois-climate-narrative.pdf |date=2008-06-25 }} Retrieved on 2008-03-19.

The 1995 Chicago heat wave was one of the worst weather-related disasters in state history, with 525 dead within a five-day period as overnight lows remained as high as {{convert|84|F|C|1}} and daytime highs reached up to {{convert|106|F|C|1}}.Illinois State Climate Office. [http://www.sws.uiuc.edu/atmos/statecli/General/1995Chicago.htm 1995 Chicago Heat Wave.] {{Webarchive|url=https://web.archive.org/web/20050313022440/http://www.sws.uiuc.edu/atmos/statecli/General/1995Chicago.htm |date=2005-03-13 }} Retrieved on 2008-02-01. The most deadly heatwave in the history of the United States struck Illinois during July 1936, which killed 2,656 people.Wayne Blanchard. [http://training.fema.gov/EMIWeb/edu/docs/hazdem/Appendix-WORST%20DISASTERS%20lives%20lost.doc WORST DISASTERS – LIVES LOST (U.S.).] Retrieved on 2008-02-01.

File:Stuck Salt Truck on Lake Shore drive Chicago Feb 2 2011 storm.JPG

Extreme temperature changes can occur within minutes with the passage of a strong cold front through the state. On December 20, 1836, temperatures fell {{convert|40|F-change|C-change|1|disp=or}} in minutes, which supposedly froze people to their saddles and chickens in their tracks.Minnesota State Climatology Office. [http://climate.umn.edu/pdf/day_in_weather_history/december_wx_history.pdf This Day in Weather History.] {{Webarchive|url=https://web.archive.org/web/20080216073411/http://climate.umn.edu/pdf/day_in_weather_history/december_wx_history.pdf |date=2008-02-16 }} Retrieved on 2008-02-01. Until 2019, the lowest temperature was {{convert|-37|F|C|1}}, recorded on January 15, 2009, at Rochelle.[http://www.wunderground.com/history/airport/KRPJ/2009/1/15/DailyHistory.html?req_city=NA&req_state=NA&req_statename=NA History for Rochelle, IL: January 15, 2009.]. Accessed 2009-01-15 However, Illinois did not officially recognize this measurement, as it was made from a small airport and there were no quality control procedures applied to the measurement.{{Cite web|url=https://www.isws.illinois.edu/statecli/General/averages.htm|title=Illinois Climate Records and Averages, Illinois State Climatologist Office, Illinois State Water Survey, U of I|website=www.isws.illinois.edu|access-date=2019-02-02}} As a result, the official record-lowest temperature for the state was {{convert|−36|F|C|1}} recorded at Congerville on 5 January 1999.Midwestern Regional Climate Center. [http://mcc.sws.uiuc.edu/climate_midwest/mwclimate_events_cold1.htm# Climate of the Midwest: Cold and Snow.] {{Webarchive|url=https://web.archive.org/web/20070506190920/http://mcc.sws.uiuc.edu/climate_midwest/mwclimate_events_cold1.htm |date=2007-05-06 }} Retrieved on 2008-02-01. In 2019, the January North American Cold Wave struck Illinois. This resulted in a new record low temperature, {{convert|−38|°F|°C|1}}, recorded on January 31, 2019, at Mount Carroll.

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Average yearly precipitation for Illinois varies from just over {{convert|48|in|mm}} at the southern tip to just under {{convert|32|in|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 Michigan leads to an increase in winter precipitation along its south shore due to lake effect snow 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.

While normal annual snowfall exceeds {{convert|38|in|m|2}} in Chicago, the southern portion of the state normally receives less than {{convert|14|in|m|2}}. The snowiest winter on record for Chicago was {{convert|89.7|in|m|2}} during the winter of 1978–79.{{cite news|work=St. Louis Post-Dispatch|title=Windy city has dodged (so far) its annua dose of big snow|author=Tammy Webber (The Associated Press)|date=2002-01-13|pages=C4}} The city has also recorded two other winters with snowfall in excess of {{convert|80|in|m|2}}—1977-78 and 2013-14. During the winter of 1830–31, southern sections of the state were covered with {{convert|3|ft|m}} of snow, with drifts up to {{convert|6|ft|m}} tall. Storms exceeding the normal winter value are possible within one day mainly in the southern half of the state. The heaviest snowfall recorded in Chicago history was {{convert|23|in|m|2}} during the Blizzard of 1967.{{cite news|title=The Deep Snow: Winter of 1830–31 has legends that Chicago's records fail to shake|work=The Illinois Intelligencer|url=http://www.illinoishistory.com/deepsnow.htm|access-date=2008-02-01|date=1968-01-28}}

{{See also|List of Illinois tornadoes}}

Illinois averages around 50 days of thunderstorm activity a year which put it somewhat above average for the 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 {{convert|10000|sqmi|km2|-4}} annually. Peak tornado activity occurs between April and June. Illinois also receives the remnants of tropical cyclones which have struck the Gulf coast. One of the wetter systems, Tropical Storm Claudette, impacted the state in July 1979 bringing rainfall amounts up to {{convert|7.64|in|mm}}.{{US States Tropical Cyclone Point Maxima}}

• Climate change in Illinois
• Cold wave
• Heat wave
• List of wettest known tropical cyclone remnants in Illinois
• List of ecoregions in Illinois

{{reflist|2}}[https://www.ncdc.noaa.gov/extremes/scec/records/IL 22. https://www.ncdc.noaa.gov/extremes/scec/records/IL]{{ClimateUS}}

Illinois