-- Chicago weather facts --

Chicago snow: On January 14, 1979, Chicago was in the midst of a 7-day period (Jan. 11-17) during which 25.6 inches of snow blanketed the city; daily totals: 0.3, 1.9, 16.5, 2.3, 2.0, 0.3, 2.3.

Chicago temperature surprise: Based on Midway and O'Hare data, daily high temperatures in the 60s occur more often in the city during December than during July.

Chicago's -20 degree days: Of the 36,524 days in the 20th Century, Chicago's temperature has fallen to -20 or lower on only ten of them: Jan. 10, 1982(-26); Jan. 16, 1982 (-25); Jan. 17, 1982 (-23); Dec. 23, 1983 (-21); Dec. 24, 1983 (-25); Jan. 20, 1984 (-20); Jan 21, 1984 (-22); Jan. 19, 1985 (-23); Jan. 20, 1985 (-27); Jan. 18, 1994 (-21).

Chicago's 4th of July weather: It's the city's warmest holiday. Normal high/low are 83/62, but it has been as hot as 102 (1911) and as chilly as 50 (1972). It rains 34 percent of the days. Wettest: 1.72 inches (1995).

Chicago's 4th of July temperatures: It's the city's warmest holiday. Normal high and low temperatures are 83 and 62, but it has been as hot as 102 (1911) and as chilly as 50 (1972). The lowest maximum temperature: 62 (1920) and the highest minimum: 80 (1921).

Chicago's 90-degree days: (1) On average, the temperature rises to 90 or higher on 17 days per year at O'Hare International Airport (45-year average); at Midway Airport, the average is 24 days per year (76 years); at the lakefront, it is 11 days (54 years).

Chicago's air pressure extremes: Lowest air pressure: 28.70 inches of mercury on March 12, 1923. Highest air pressure: 30.98 inches of mercury on February 16, 1989.

Chicago's annual statistics: (O'Hare data) Average annual temperature: 49.0 degrees; average high: 58.6; average low: 39.5; precipitation: 35.82 inches; snowfall: 38.7 inches; days 0 or lower: 12; days 90 or higher: 18.

Chicago's April temperature extremes: Based on official records dating from 1871, Chicago's temperatures in April have ranged from 91 (April 22, 1980, and April 30, 1942) to 7 (April 7, 1982).

Chicago's August precipitation extremes: In records dating from 1871, greatest: 17.10 inches in 1987 (this is also the greatest total for any month); least: 0.18 inches in 1893.

Chicago's August winds: Based on Midway Airport data, Chicago's winds in August blow from the north, northeast or east 29 percent of the time and at an average speed of 7 m.p.h.

Chicago's autumn snow records: In records dating from 1884, Chicago's earliest trace of snow: September 25 in 1928 and also 1942; earliest inch of snow: 1.8 inches on October 19, 1989 (recorded at Midway Airport).

Chicago's average cold arrival dates in autumn: Using Midway data (1928-2003), Chicago experiences its first autumn temperature in the 30s on Oct. 5; freezing (32 degrees) on Oct. 23; in the 20s on Nov. 2.

Chicago's average first freeze date: The average date of Chicago's first freezing temperature in the autumn varies considerably across the metropolitan area, occurring earliest in outlying areas and latest downtown. The range is from October 11 (O'Hare) to November 6 (Loop).

Chicago's Christmas Eve weather extremes: Mildest: 64 degrees, 1889; coldest: -25, 1983; snowiest: 7.1 inches, 1918; rainiest: 2.61 inches, 1965 (also 1/2 inch of snow); windiest: 49 m.p.h. from the southwest, 1932.

Chicago's Christmas weather extremes: Mildest: 64/3° (1982); coldest: -5/-17 (1983); snowiest: 5.1 inches (1950) and 5.0 inches (1909); biggest two-day snowstorm: 8.6 inches (Dec. 24-25, 1951) and 7.5 inches (Dec. 24-25, 1918).

Chicago's Christmas weather extremes: Mildest: 64 degrees (1982); coldest: -17 (1983); snowiest: 5.1 inches (1950); deepest snowcover: 17 inches (1951); chance of a white Christmas (snow on ground at least 1 inch): 4 in 10.

Chicago's Christmas weather statistics: Normal high/low: 31/16; highest temperature: 64 (1982); lowest temperature: -17 (1983); biggest snow: 5.1 inches (1950); deepest snowcover: 17 inches (1951); chance of a white Christmas (snow on ground at least 1"): 4 in 10.

Chicago's coldest 31 consecutive days: With an average temperature of 5.4 degrees F, the 31-day period from Jan. 20 through Feb. 19, 1936, ranks as Chicago's coldest 31-day period in official records dating from 1870.

Chicago's coldest week of the year: Based on climatological normal temperatures, the seven-day period, January 15-21, is the city's coldest week with an average temperature of 20.4 degrees.

Chicago's December snow statistics: 117-year (1885-2001) average: 10.4 inches; greatest: 41.3 inches (2000, Midway Airport); least 0.0 inches (1889 and 1912, downtown); average number of days with 1.0 inch or more: 2.

Chicago's December temperature extremes: In official records dating from 1870, Chicago's temperatures have ranged 96 degrees from 71 (Dec. 2, 1982, and Dec. 3, 1970) to -25 (Dec 24, 1983).

Chicago's earliest 0-degree event in autumn: On Nov. 23 in 1950, Chicago's temperature plunged to -1, the earliest-occurring 0 or lower temperature in the autumn in official weather records dating from 1870.

Chicago's earliest 80-degree event in the spring: On March 3, 1974, the city's temperature soared to 80, as recorded at Midway Airport. This is the earliest-occurring spring temperature of 80 or higher in the city's official temperature records dating from 1871.

Chicago's earliest autumn snow: On September 25 in 1928 and also in 1942, a trace of snow was observed in Chicago -- the earliest occurring autumn snow in the city's weather history.

Chicago's extreme short-term temperature change: (1) A 22-degree drop in 150 seconds beginning at 1:47 p.m. CDT, May 9, 1963, at Grant Park, with a cold frontal passage and wind shift off chilly Lake Michigan waters. (2) On May 9, 1963, a strong cold front surged across Chicago. Aided by a wind shift off the cold late-spring waters of Lake Michigan, the temperature at Grant Park plunged 22 degrees (from 84 to 62) in 150 seconds beginning at 1:47 p.m. CDT.

Chicago's February snowfall statistics: 119-year average (1885-2003) 8.5 inches; greatest: 27.8 inches in 1896; least: trace in 1998; biggest snowstorm 13.4 inches Feb. 6-7, 1895.

Chicago's February temperature extremes: A range of 96 degrees from 75 recorded on Friday, Feb. 27, 1976, at Midway Airport, to -21 recorded on Thursday, Feb. 9, 1899, in downtown Chicago.

Chicago's first 70-degree day in spring: On average, it occurs on March 31. It has happened as early as February 11 (1999) and has been delayed as late as May 7 (1874).

Chicago's first autumn freeze: At O'Hare Airport, the average date of the first autumn temperature of 32 degrees or lower is October 11.

Chicago's first autumn snow: Based on 74 years of data (1928-2001) at Midway Airport, the average date of Chicago's first flake of snow in the autumn is October 31.

Chicago's first fall freeze: On average, Chicago's first fall temperature of 32 degrees or lower occurs on October 12 at O'Hare, October 24 at Midway and November 6 in the Loop.

Chicago's frequency of 90-degree days: On average, Chicago's temperature climbs to 90 or higher on 17 days per year, but within about one mile of Lake Michigan, due to the cooling influence of the lake, the number is only 10 days per year.

Chicago's greatest May rain: 3.30 inches on Wednesday, May 11, 1966. The greatest two-day rainstorm: 3.80 inches on May 11-12, 1966.

Chicago's greatest snow depth: 29 inches of snow on the ground at Midway Airport on Jan. 14, 1979 -- resulting from 13 inches of snow in the final days of 1978 and 21 inches of snow from Jan. 11-14, 1979, and frigid temperatures that prevented melting.

Chicago's greatest temperature changes: Officially, 132-degree range from 105 on July 24, 1934, to -27 on January 20,1985; greatest daily range, 52 degrees (high/low of 62/10 on February 8, 1900); day-to-next change, 61 degrees (from 74 on November 11, 1911, to 13 on the 12th).

Chicago's growing season: Depending on the location in the metropolitan area, Chicago's growing season (the number of days between the last spring and first fall occurrences of 32 degrees) is about 186 days in length. This year, Chicago's growing season ended on October 7, at 168 days.

Chicago's growing season: The length of Chicago's growing season (the number of days between the last spring and first autumn occurrences of 32 degrees) ranges from about 170 days in outlying locations to 200 days in the central city.

Chicago's Halloween weather extremes: Mildest: 84 degrees (1950, Midway); coldest: 23 (1873; downtown); wettest: 2.63 inches (1994, Midway); heaviest snow: trace (1890, 1917, 1918, 1926, 1955, 1993).

Chicago's heaviest 24-hour rainfall: (1) 9.35 inches. On Aug. 13, 1987, the heaviest 24-hour rain ever officially recorded in Chicago began. 2.86 inches of rain fell at the O'Hare weather observation station before midnight on the 13th and 6.49 inches fell as rain continued on the 14th.

Chicago's heaviest April rainfall: 4.48 inches on April 4-5, 1947. In 132 Aprils (1871-2002), Chicago has experienced 172 storms that delivered 1.00 inch or more of precipitation.

Chicago's heaviest April snowstorm: 10.7 inches on April 1-2, 1970. In 117 Aprils (1886-2002), Chicago has experienced seven storms that delivered 5.0 inches or more of snow.

Chicago's heaviest rain: On August 13-14, 1987, a deluge of 7-11 inches of rain swept across northwest metropolitan Chicago. 9.35 inches of rain was recorded at O'Hare International Airport, the heaviest official 24-hour rain event in the city's history.

Chicago's heaviest snow: The greatest snowstorm ever to occur in Chicago began on Jan. 6, 1967. The 29-hour duration of the storm brought 23.0 inches of wind-driven snow to the city. Water content of the snow was 2.40 inches, giving a snow-to-water ratio of 10:1.

Chicago's heaviest snows: In an hour: 3.5 inches during the evening of Feb. 23, 1967; in a single storm: 23.0 inches, Jan. 26- 27, 1967; in a month: 42.5 inches, Jan., 1918; in a snow season: 89.3 inches, autumn-winter-spring of 1978-79.

Chicago's highest air pressure: On February 16, 1989, the air pressure at Chicago rose to 30.98 inches of mercury, the highest air pressure ever recorded in the city.

Chicago's highest dew point temperature: At 7:59 a.m. on July 30, 1999, the dew point temperature at O'Hare International Airport climbed briefly to 83 degrees, the highest ever officially observed in the city. This is the greatest amount of atmospheric moisture ever measured at Chicago.

Chicago's highest official temperature: (1) On July 24, 1934, Chicago's temperature soared to 105 degrees, the highest temperature ever officially observed in the city. The observation location at that time was Rosenwald Hall, 58th St. and University Ave, at the University of Chicago. (2) On July 23, 1934, the temperature soared to an incredible 109 degrees at Chicago's Midway Airport -- the highest temperature ever recorded at a Chicago location. The city's official station, located then at the University of Chicago, reached only 94 degrees because it was cooled by a lake breeze.

Chicago's highest unofficial temperature: On July 23, 1934, the temperature at Midway Airport soared to 109 degrees, the highest temperature ever recorded in Chicago. The reading is considered unofficial because the city's observation station for climatological and record purposes was at that time located at the University of Chicago (which measured a high temperature of 94 degrees).

Chicago's highest wind gust: 88 m.p.h. from the northwest, on August 27, 1965, at 3:45 a.m. CDT, as measured by observer Frank Wachowski at the Midway Airport weather observation station.

Chicago's hottest day: (1) With an average temperature of 93 degrees (based on a high of 102 and a low of 84), Sunday, July 30, 1916, stands as Chicago's hottest day in official temperature records dating from 1871. (2) With an average temperature of 94 degrees (based on a high of 104 and low of 84 as recorded at Midway Airport), Friday, July 30, 1999, is Chicago's hottest day in records dating from 1871; this is considered to be unofficial because Midway was then not the official station.

Chicago's hottest week: July 19-25, 1934, with an average temperature of 89.1 degrees, as recorded at Midway Airport. The daily high/low readings that week: 99/69 103/71 108/73 104/74 109/74 107/77 105/74.

Chicago's January snowfall extremes: In snowfall records dating from 1885, the city's January snowfall extremes are: (least) 0.2 inch in 1928 and 0.3 inch in 1900 and 1934; (greatest) 42.5 inches in 1918 and 40.4 inches in 1979.

Chicago's January temperature extremes: A range of 94 degrees from 67 recorded on Wednesday, Jan. 25, 1950, at Midway Airport, to -27 recorded on Sunday, Jan. 20, 1985, at O'Hare International Airport.

Chicago's July 4th extremes: Highest maximum 102 degrees (1911); lowest maximum 62 (1920); lowest minimum 50 (1972); highest minimum 80 (1921); heaviest rain 1.72 inches (1995).

Chicago's July precipitation extremes: In records dating from 1871, greatest: 9.56 inches in 1889; least: 0.22 inches in 1936. Greatest July rainstorm: 6.24 inches on July 12-13, 1957.

Chicago's July temperature extremes: Highest is 109 degrees (and also the highest in any month), observed at Midway Airport on the 23rd in 1934; lowest is 45 on the 7th in 1983, observed at O'Hare Int'l. Airport.

Chicago's June temperature extremes: Based on official temperature records dating from 1873, Chicago's temperatures in June have ranged from 104 degrees (June 20, 1953 and 1988) to 35 (June 4, 1945).

Chicago's largest two-day temperature change in April: Spring temperatures can change on a dime, but the largest two-day April temperature change is 56 degrees, from 29 (April 9, 1977) to 85 on the 10th.

Chicago's late-April snow: Although rare, late-April snow does occur in Chicago. At this time in 1910, intermittent snow over a 5-day period brought 6.4 inches of snow to the city. Chicago's daily snowfall totals April 22-26, 1910: 0.1", 2.1", 0.9", 2.5", 0.8".

Chicago's late-March temperature extremes: Since 1871, the city's temperatures in the last week of March have been as high as 88 degrees (Mar. 29, 1986) and as low as 7 (Mar. 27, 1873).

Chicago's latest 70-degrees temperature: On Dec. 3, 1970, Chicago's temperature soared to 71 degrees, the latest occurring 70-degrees or higher reading in official weather records dating from 1870.

Chicago's latest 80+ temperature: On today's date (Nov. 1) in 1950, Chicago's temperature soared to 81 degrees, the latest occurring 80+ reading in official weather records dating from 1872.

Chicago's latest 90-degree or higher temperature: On Oct. 6, 1963, Chicago's temperature soared to 94 degrees, the latest-occurring 90+ reading in official weather records dating from 1872.

Chicago's latest measurable snow: On May 11, 1966, 0.2 inches of snow was officially recorded at Midway Airport during the early morning hours. Two inches of snow were observed in suburban areas. The day's high/low temperatures were 45/34, and heavy rain (in excess of three inches) caused widespread metropolitan flooding.

Chicago's latest spring freeze: The average date of the city's last-occurring spring temperature 32-degree or less is April 18, but a freeze has occurred here as late as May 25 (32 on May 25, 1992).

Chicago's latest spring snow: On May 11, 1966, 0.2 inches of snow was observed at Midway Airport, the city's latest measurable snow; on June 2, 1910, a trace of snow occurred in downtown Chicago. High/low temperatures that day, 55/43 degrees; precipitation, 0.41 inches from rain, hail and a trace of snow.

Chicago's longest dry spell: 30 days without measurable precipitation (0.01 inch or more), extending from January 7 through February 5, 1919.

Chicago's longest zero spell: 100 hours (four days, four hours). Beginning at 7 a.m. on December 22, 1983, and continuing through Christmas Eve and Christmas Day to 11 a.m. on December 26, Chicago's temperature remained at or below zero for 100 consecutive hours, the longest frigid spell in the city's history.

Chicago's lowest air and wind-chill temperatures: -27 degrees and -93 degrees, respectively, both recorded in the morning hours of Sunday, January 20, 1985, when biting northwest winds 25 to 35 m.p.h. blasted across the city.

Chicago's lowest air pressure: On this date in 1923 (March 12), the lowest air pressure ever recorded in Chicago, 28.70 inches of mercury, was set during a wintry storm that was accompanied by 60 m.p.h. northeast winds, freezing rain, sleet and 1.2 inches of snow. High/low temperatures that day were 41 and 31.

Chicago's lowest November temperature: On November 24, 1950, Chicago experienced its lowest November temperature (-2 degrees) since records began in 1870.

Chicago's lowest relative humidity: In weather records dating from 1871, the city's lowest relative humidity is 13 percent on three occasions: May 10, 1934; April 11, 1956; April 8, 1971.

Chicago's lowest temperature: On January 20, 1985, the temperature plummeted to an incredible -27 degrees at O'Hare International Airport, the lowest temperature ever recorded at an official Chicago location.

Chicago's lowest temperature at the start of a new year: As 11:59 p.m., December 31, 1967, changed to January 1, 1968, Chicago's temperature was -9 degrees F., the lowest temperature ever observed in the city at the start of a new year.

Chicago's lowest wind-chill temperature: Bitterly cold temperatures and vicious winds gripped Chicago on January 20, 1985. Early-morning temperatures between -20 and -27 in combination with biting northwest winds 25 to 35 m.p.h. briefly produced a wind-chill temperature of -93 degrees, the lowest ever recorded in Chicago.

Chicago's March temperature extremes: Based on official temperature records dating from 1871, Chicago's temperatures in March have ranged from 88 degrees (March 29, 1986) to -12 (March 4, 1873).

Chicago's moisture deficit: The Palmer Drought Severity Index classifies drought in three stages of increasing severity: moderate, severe, extreme. Chicago's moisture deficit now: moderate drought.

Chicago's most violent and destructive event: Seven tornadoes (three of them killers) touched down across metropolitan Chicago on April 21, 1967. 58 lives were lost and 1,100 injured in Belvidere, Lake Zurich, Oak Lawn and Hometown. Damage: $100 million.

Chicago's New Year's Day weather extremes: Mildest: 65/40 (1876); coldest: 5/-10 (1969); snowiest: 5.0 inches (1918); biggest two-day snowstorm: 20.6 inches (Jan 1-2, 1999).

Chicago's November temperature data: Average temperature: 40.0 degrees. In records dating from 1870, November, 1931, is the city's warmest with an average temperature of 50.0 degrees; November, 1880, the coldest at 31.6 degrees.

Chicago's November temperature extremes: In official records dating from 1870, Chicago's temperatures in November have ranged from 81 degrees (Nov. 1, 1950) to -2 (Nov. 24, 1950, and Nov. 29, 1872).

Chicago's October precipitation records: October normal: 2.41 inches; wettest: October of 1954 with 12.03 inches; driest: October of 1897 with 0.18 inches. Total precipitation so far this October: 5.99 inches (249 percent of full-month normal).

Chicago's October temperature extremes: Based on official temperature records dating from 1871, Chicago's temperatures in October have ranged from 94 degrees (October 6, 1963) to 14 (October 25, 1887).

Chicago's second-highest temperature: On this date (June 20) in 1953 and 1988, Chicago's temperature surged to 104 degrees, the second-highest reading ever recorded in the city in official temperature records dating from 1871.

Chicago's second-lowest temperature: On January 10, 1882, Chicago's temperature plunged to 26 degrees below zero, the second-lowest temperature ever recorded in the city since official records began in 1870. Six days later (Jan. 16, 1982)

Chicago's September, 1871, drought: Only 0.74 inches of rain (one-fifth of normal) fell in the five weeks prior to the start of the Great Chicago Fire on October 8, 1871. Normal rainfall in the period is 3.79 inches.

Chicago's September temperature extremes: Based on official records dating from 1871, Chicago's September temperatures have ranged from 101 degrees (1st and 2nd, 1953) to 29 (23rd, 1995; 28th, 1942; 30th 1984).

Chicago's snow extremes: Greatest snowstorm, 23.0 inches January 26-27, 1967; snowiest and least-snowy winters, 89.7 inches 1978/79 and 9.8 inches 1920/21; greatest snow depth on ground, 29 inches January 14, 1979.

Chicago's snowiest December: December, 2000, when 41.3 inches came down (as measured at Midway Airport). 117-year average Dec. snowfall: 10.4 inches.

Chicago's snowiest January: January, 1918, when 42.5 inches came down (as measured at the U.S. Courthouse Building, 219 S. Clark Street in downtown Chicago, the official weather observation station for the city at that time). The long-term average January snowfall: 10.1".

Chicago's snow season: July and August are the city's only totally snow-free months. Traces of snow have fallen as late as June 2, 1910, and as early as September 25, 1928 and 1942. Because June is considered to be a summer month, it is true that snow has occurred here in every season.

Chicago's Thanksgiving weather extremes: Highest/lowest temperatures: 69 degrees (Nov. 24, 1966) and -1 (Nov. 23, 1950); heaviest snow 3.0 inches (Nov. 27, 1980); heaviest rain 1.56 inches (Nov. 28, 1968); normal high/low: 43/28; measurable precipitation: four days of 10; measurable snow: one of six.

Chicago's wettest month: August, 1987, when 17.10 inches of rain fell (as measured at O'Hare International Airport, the location of the city's official weather observation station).

Chicago's windiest place: Arguably, the northeast corner of Jackson and Wabash. Other challengers for the windiest location: Michigan and Oak; Columbus and Randolph; the IBM and Equitable Plazas.

Chicago's winter temperature extremes: Based on official temperature records dating from 1871, the city's highest winter temperature is 75 degrees (February 27, 1976) and the lowest is -27 (January 20, 1985); that is a range of 102 degrees.

Chicago's worst drought: (1) The spring and summer of 1934, when only 4.65 inches of precipitation (or 32 percent of normal) fell during the period April 1-July 31, a critical period for agriculture.

Chicago's worst shoreline damage: On February 8, 1987, 50-70 m.p.h. north winds produced 12-18 foot waves over south Lake Michigan, causing $7 million flood and erosion damage along the Chicago area shoreline.

Chicago's zero temperatures in December: Zero degrees or lower has occurred in 52 percent of Chicago Decembers since 1871.

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