Climate of Chicago

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Chicago
Climate chart (explanation)
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Average max. and min. temperatures in °F
Precipitation totals in inches
Source: NOAA
 
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Downtown Chicago in the winter

The climate of Chicago is classified as humid continental climate (Köppen Dfa), with all four seasons distinctly represented: wet springs; hot, and often humid summers; pleasant autumns; and cold winters. Annual precipitation is average, and reaches its lowest points in the months of January and February, and peaks in the months of May and June.

Contents

Data

Seasons

Winter

Winter in Chicago proves quite variable and fickle, but the city's cold winters will have bouts of mild days strung together every so often. The average Chicago winter produces 38.0 inches (970 mm) of snow. This is just an average; Chicago winters have produced as little as 9.8 inches (250 mm) and up to 89.7 inches (2,280 mm) of snow. Most winters produce only a few snow falls during the season in light accumulations of around 2 inches (51 mm), but about every three years or so the city may experience a snowstorm that can produce over 10 inches (250 mm) of snow over a 1-3 day period. Unlike across Lake Michigan in western Michigan or in northern Indiana, Chicago rarely gets lake-effect snow because prevailing westerlies that cross the region pick up moisture from Lake Michigan after passing Chicago. Rare northeasterly winds during the winter may deposit the sort of snowfall that one associates with nearby snowbelt cities such as Grand Rapids, Michigan, Kalamazoo, Michigan, and South Bend, Indiana with the more usual westerly winds. Temperatures can vary wildly within the span of one week, but temperatures can often stay below freezing for several consecutive days or even weeks in January and February. The temperature in January averages about 29 °F (−2 °C) in the afternoon, and 14 °F (−10 °C) at night. Temperatures can be expected to drop below 0 °F (−18 °C) on about 15 nonconsecutive days throughout the winter season. On many occasions temperatures can go above 50 °F (10 °C) for a daytime high, and, although not frequent, temperatures in winter can surpass 60 °F (16 °C).

Summer

On a typical summer day, humidity is usually moderately high and temperatures ordinarily reach anywhere between 78 and 92 °F (26 and 33 °C). Overnight temperatures in summer usually drop to around 65 °F (18 °C)-70 °F (21 °C). Yearly precipitation comes in at an average of about 36 inches (910 mm). Summer in Chicago is prone to thunderstorms, and summer rain arises from short-lived hit-or-miss rain rather than actual prolonged rainfalls, thunderstorms also occur with regularity at night. In a normal summer, temperatures exceed 90 °F (32 °C) on 23 days. Contrary to what one might think, summer is actually the rainiest season in Chicago.[4] In a curious shift, July was actually the wettest average month in Chicago from when records were started in 1871 until 1965. In 1965, August inexplicably overtook July as the wettest month, and it currently remains wetter than July.

In July 2012, Chicago temperatures reached more than 100 degrees for three days in a row with highs reaching 103 degrees. It was the first time Chicago had ever seen a triad of 100-degree days.[5]

Temperature Extremes

Chicago
Climate chart (explanation)
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2
 
31
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1.8
 
36
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2.8
 
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3.8
 
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3.9
 
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4.2
 
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3.8
 
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3.5
 
75
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2.8
 
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3.2
 
48
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Average max. and min. temperatures in °F
Precipitation totals in inches
Source: NOAA

The highest temperature ever recorded in Chicago is an unofficial 109 °F (43 °C) on July 24, 1934 at Midway Airport. The official readings then were taken at the University of Chicago campus near the waterfront. Readings near the lake can be several degrees cooler than inland locations if lake breezes are present. The highest official temperature ever recorded is 107 °F (42 °C) also on July 24, 1934. During the Chicago Heat Wave of 1995, temperatures reached 104 °F (40 °C) officially at O'Hare Airport and 106 °F (41 °C) at Midway, but humidity made temperatures feel almost as hot as 120 °F (49 °C) at O'Hare and 125 °F (52 °C) at Midway. The coldest temperature ever recorded in Chicago is −27 °F (−33 °C) on January 20, 1985. On December 24, 1983, and January 18, 1994, the high temperature at Chicago reached only −11 °F (−24 °C), and on July 29, 1916, the low temperature sank to only 85 °F (29 °C), both of which are records.

Windy City

Although Chicago is known as the Windy City, it is in fact less windy than many other major American cities. Average wind speeds range from 8 miles per hour (13 km/h) in late summer to 12 miles per hour (19 km/h) in spring months. The "Windy City" moniker is actually believed to be a reference to the boostering politicians of Chicago from the 1800s. The phrase may have also been created by Chicago tourism boosters promoting the city, cooled off by breezes from Lake Michigan, as an ideal summer destination.

Lake Breeze

Chicago experiences microclimatic effects because of relative chillier waters of Lake Michigan, these effects are most pronounced during spring and early summer. Very often a local lakeshore breeze pulls much cooler, moist air into Chicago than the usual hot air of the Plains States (usually a moist air mass depending on upper level circulation), but the effect may be so localized that only the immediate waterfront neighborhoods (especially northern lakeside communities) are cooler than inland parts of the city. South and southwestern suburbs are sometimes 20 °F (11 °C) or more warmer under these conditions. The lake breeze also has other effects, including dense fog spilling into the city. Because of the closed-loop circulation pattern with a lake breeze that moves back and forth across the city, it is thought to significantly increase low-level ozone counts. [6] Differing wind direction on either side of the thermal dividing line allows for sharp updrafts under certain conditions, favorable to thunderstorm development. Offshore or land breezes shutdown the lake breeze and can have the opposite effect, with over lake convection occurring, usually in mid-late summer and fall. As a general rule, winter temperatures are warmer along the lakeshore and downtown than inland, but the lake can increase storm intensity.

References

  1. ^ "NowData - NOAA Online Weather Data". National Oceanic and Atmospheric Administration. http://www.nws.noaa.gov/climate/xmacis.php?wfo=lot. Retrieved 2011-12-14. 
  2. ^ "Monthly Averages for Chicago, IL". The Weather Channel. http://www.weather.com/outlook/travel/vacationplanner/wxclimatology/monthly/USIL0225. Retrieved 2011-12-14. 
  3. ^ "Climatological Normals of Chicago". Hong Kong Observatory. http://www.hko.gov.hk/wxinfo/climat/world/eng/n_america/us/chicago_e.htm. Retrieved 2010-05-12. 
  4. ^ Chicago Summer Precipitation Rankings Summer (June-August) (11/29/2005). NOAA's National Weather Service Forecast Office.
  5. ^ "Chicago Heat Wave: Friday Completes City's First Triad Of 100-Degree Days Since 1947". http://www.huffingtonpost.com/2012/07/06/chicago-heat-wave-friday-_n_1653812.html. Retrieved 11 July 2012. 
  6. ^ ""Chicago Lake Breeze Effect Could Increase Asthma Risk"". Science Daily. http://www.sciencedaily.com/releases/2003/06/030603083134.htm.