Climate of Chicago

Downtown Chicago in the winter

Chicago
Climate chart (explanation)
J F M A M J J A S O N D     2   31 16     1.8   36 21     2.8   47 31     3.8   59 40     3.9   71 51     4.2   81 61     3.8   85 66     3.9   82 65     3.5   75 57     2.8   63 45     3.2   48 34     2.8   36 22 Average max. and min. temperatures in °F Precipitation totals in inches Source: NOAA
Metric conversion J F M A M J J A S O N D     50   -1 -9     45   2 -6     72   9 -1     97   15 5     98   22 11     106   27 16     97   29 19     99   28 18     88   24 14     71   17 7     82   9 1     70   2 -5 Average max. and min. temperatures in °C Precipitation totals in mm

Chicago has a humid continental climate (Köppen Dfa), with all four seasons distinctly represented: mild springs; hot, and often humid summers; crisp autumns; and cold winters. Annual precipitation is average, and reaches its lowest points in the months of February and January, and peaks in the months of August and April.

Data

Climate data for Chicago (Midway Airport)
Month	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Record high °F (°C)	67 (19)	75 (24)	86 (30)	92 (33)	102 (39)	107 (42)	107 (42)	103 (39)	102 (39)	94 (34)	81 (27)	71 (22)	107 (42)
Average high °F (°C)	30.7 (−0.72)	36.1 (2.3)	47.4 (8.6)	59.2 (15.1)	71.3 (21.8)	80.8 (27.1)	84.7 (29.3)	82.3 (27.9)	75.1 (23.9)	63.2 (17.3)	48.0 (8.9)	35.6 (2.0)	59.5
Average low °F (°C)	16.2 (−8.8)	21.3 (−5.9)	30.6 (−0.78)	40.2 (4.6)	50.9 (10.5)	60.7 (15.9)	66.3 (19.1)	65.0 (18.3)	56.7 (13.7)	44.9 (7.2)	33.6 (0.9)	22.2 (−5.4)	42.4
Record low °F (°C)	−25 (−31.7)	−20 (−28.9)	−7 (−21.7)	10 (−12.2)	28 (−2.2)	35 (2)	46 (8)	43 (6)	29 (−1.7)	20 (−6.7)	−3 (−19.4)	−20 (−28.9)	−25 (−31.7)
Precipitation inches (mm)	1.95 (49.5)	1.78 (45.2)	2.83 (71.9)	3.82 (97)	3.86 (98)	4.16 (105.7)	3.82 (97)	3.91 (99.3)	3.45 (87.6)	2.79 (70.9)	3.22 (81.8)	2.76 (70.1)	38.35 (974.1)
Snowfall inches (cm)	12.9 (32.8)	10.3 (26.2)	6.0 (15.2)	1.4 (3.6)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	0.1 (0.3)	2.3 (5.8)	10.1 (25.7)	43.1 (109.5)
Avg. precipitation days (≥ 0.01 in)	11.2	8.9	11.7	11.6	11.0	10.3	9.5	9.6	8.9	9.7	11.5	11.3	125.2
Avg. snowy days (≥ 0.1 in)	6.2	6.2	4.5	1.0	0.1	0	0	0	0	0.2	2.7	7.2	30.5
Sunshine hours	136.4	138.4	186.0	216.0	282.1	312.0	319.3	282.1	228.0	192.2	114.0	105.4	2,511.9
Source no. 1: Illinois State Climatologist Office (normals 1971−2000, extremes 1928−2006) [1]
Source no. 2: HKO (sun only, 1961−1990) [2]

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 (94 cm) of snow. This is just an average; Chicago winters have produced as little as 9.8 of snow, up to 89.7 inches (25 cm and 221 cm) of snow. Most winters produce only a few snow falls during the season in light accumulations of around 2 inches (5 cm), but about every three years or so the city may experience a snowstorm that can produce 10 or more inches (25 cm to 35 cm) 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 40° for a daytime high, and, although not frequent, temperatures in winter can surpass 50°F (10°C). l

Summer

On a typical summer day, humidity is usually moderately high and temperatures ordinarily reach anywhere between 78°F and 92°F (26°C to 33°C). Overnight temperatures in summer usually drop to around 65°F (18°C), but can sometimes hover around 70°F (21°C). Yearly precipitation comes in at an average of about 36 inches (920 mm). Summer in Chicago is prone to thunderstorms, and summer rain arises from short-lived hit-or-miss rain rather than actual prolonged rainfalls. 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.^[3] 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.

Temperature Extremes

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 105°F (41°C) also on July 24, 1934. During the Chicago Heat Wave of 1995, temperatures reached 104°F officially at O'Hare Airport and 106°F at Midway, but humidity made temperatures feel almost as hot as 120°F. 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 (-23°C), and on July 29, 1916, the low temperature sank to only 85°F (29°C), both of which are records.

Moniker

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 mph (13 km/h) in late summer to 12 mph (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.

Chicago experiences microclimatic effects because of Lake Michigan, especially during the summer. Very often during the summer a local lakeshore breeze pulls much cooler air into Chicago than the usual hot air of the Plains States, but the effect may be so local that only the immediate waterfront neighborhoods are cooler than inland parts of the city.

According to the U.S. Department of Agriculture, Chicago falls within Plant Hardiness Zone 5b, with the outlying areas falling into the sightly harsher Zone 5a.^[4] The Arbor Day Foundation has issued an updated plant hardiness zone map that places the lakefront and southern suburbs into the upper reaches of Zone 6.^[5]

References

1. ^ "Historical Climate Data Chicago Midway Airport (1971-2000)". Illinois State Climatologist Office. http://www.isws.illinois.edu/atmos/statecli/Summary/illinois.htm. Retrieved 2009-11-10. 
2. ^ "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. 
3. ^ Chicago Summer Precipitation Rankings Summer (June-August) (11/29/2005). NOAA's National Weather Service Forecast Office.
4. ^ US National Arboretum - USDA Plant Hardiness Zone Map (2/23/2004). United States Department of Agriculture.
5. ^ "New arborday.org Hardiness Zone Map reflects warmer climate : Latest hardiness zones, based on most current temperature data available, suggest up-to-date choices for best trees to plant". http://www.arborday.org/media/zonechanges2006.cfm. Retrieved 2007-12-27.