Historical Climate Data

Precipitation Summary

Station: 111549 CHICAGO OHARE AP, IL

1971-2000 NCDC Normals

Element Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann
Prec. (in) 1.75 1.63 2.65 3.68 3.38 3.63 3.51 4.62 3.27 2.71 3.01 2.43 36.27

Precipitation Extremes

Period of Record: 1958-2006


Month
High (in)
Year
Low (in)
Year 		1-Day
Max (in)
Date
Jan 4.47 1999 0.10 1981 2.00 01-12-1960
Feb 5.56 1997 0.12 1969 3.44 02-21-1997
Mar 5.91 1976 0.63 1981 1.75 03-04-1985
Apr 7.69 1983 0.74 2004 2.37 04-20-2000
May 7.22 2004 0.30 1992 3.45 05-29-1981
Jun 9.96 1993 0.76 2005 3.09 06-10-1967
Jul 8.33 1982 1.18 1977 2.90 07-18-1993
Aug 17.10 1987 0.51 1969 6.49 08-14-1987
Sep 11.44 1961 0.02 1979 2.88 09-13-1961
Oct 8.54 2001 0.16 1964 4.25 10-10-1969
Nov 8.22 1985 0.44 1999 2.93 11-27-1990
Dec 8.56 1982 0.23 1962 4.47 12-02-1982
             
Annual 49.35 1983 21.77 1962 6.49 08-14-1987
Winter 11.28 1983 1.43 1963 4.47 12-02-1982
Spring 17.51 1983 3.87 1994 3.45 05-29-1981
Summer 23.48 1987 5.08 1991 6.49 08-14-1987
Fall 16.54 1961 3.10 1962 4.25 10-10-1969

Precipitation Threshold Climatology

Derived from 1971-2000 Averages:

*Annual/seasonal totals may differ from the sum of the monthly totals due to rounding.


Month 		# Days
Total ≥ 0.01" 		# Days
Total ≥ 0.10" 		# Days
Total ≥ 0.50" 		# Days
Total ≥ 1.00"
Jan 11.3 4.9 0.9 0.2
Feb 9.3 4.1 0.8 0.2
Mar 11.7 6.2 1.4 0.4
Apr 12.6 6.9 2.3 0.9
May 11.4 6.8 2.3 0.6
Jun 10.1 6.1 2.7 1.0
Jul 9.5 6.1 2.3 1.0
Aug 10.1 6.7 2.9 1.3
Sep 8.8 5.5 2.1 0.9
Oct 9.5 5.2 1.8 0.5
Nov 11.4 6.2 1.7 0.6
Dec 11.2 5.2 1.3 0.5
         
Annual 127.0 69.9 22.4 8.2
Winter 31.8 14.2 2.9 0.9
Spring 35.7 19.9 6.0 2.0
Summer 29.8 18.9 7.8 3.3
Fall 29.7 16.9 5.6 2.0

Temperature Summary

Station 111549 CHICAGO OHARE AP, IL

1971-2000 NCDC Normals

Element Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann
High °F 29.6 34.7 46.1 58.0 69.9 79.2 83.5 81.2 73.9 62.1 47.1 34.4 58.3
Low °F 14.3 19.2 28.5 37.6 47.5 57.2 63.2 62.2 53.7 42.1 31.6 20.4 39.8
Mean °F 22.0 27.0 37.3 47.8 58.7 68.2 73.3 71.7 63.8 52.1 39.3 27.4 49.1
HDD 1333 1075 858 513 232 49 6 9 112 401 759 1151 6498
CDD 0 0 1 9 48 159 279 233 91 10 0 0 830

HDD - heating degree days (base 65F); CDD - cooling degree days (base 65F)

Temperature Extremes

Period of Record: 1958-2006


Month 		High
Mean °F
Year 		Low
Mean °F
Year 		1-Day
Max °F
Date 		1-Day
Min °F
Date
Jan 35.8 2006 10.7 1977 65 01-31-1989 -27 01-20-1985
Feb 38.7 1998 16.2 1979 72 02-25-2000 -19 02-03-1996
Mar 44.9 1977 24.4 1960 88 03-29-1986 -8 03-01-1962
Apr 55.0 1977 43.3 1975 91 04-22-1980 7 04-07-1982
May 67.2 1977 53.2 1983 93 05-19-1977 24 05-10-1966
Jun 74.2 2005 62.1 1982 104 06-20-1988 36 06-22-1963
Jul 78.4 1999 68.4 1967 104 07-13-1995 40 07-01-1965
Aug 79.0 1995 66.2 1967 101 08-02-1991 41 08-15-1964
Sep 69.7 1971 59.2 1993 99 09-07-1960 28 09-23-1974
Oct 61.7 1971 46.1 1988 91 10-06-1963 17 10-24-1981
Nov 48.2 2001 31.8 1959 78 11-05-1978 1 11-30-1958
Dec 36.0 1982 13.3 1963 71 12-02-1982 -25 12-24-1983
                 
Annual 53.6 1998 47.1 1985 104 06-20-1988 -27 01-20-1985
Winter 33.1 1998 17.2 1963 72 02-25-1900 -27 01-20-1985
Spring 55.7 1977 43.6 1984 93 05-19-1977 -8 03-01-1962
Summer 76.4 1995 67.1 1992 104 06-20-1988 36 06-22-1963
Fall 57.7 1971 47.8 1976 99 09-07-1960 1 11-30-1958

Temperature Threshold Climatology

Derived from 1971-2000 Averages:

*Annual/seasonal values may differ from the sum of the monthly values due to rounding.


Month 		# Days
High ≥ 90°F 		# Days
High ≤ 32°F 		# Days
Low ≤ 32°F 		# Days
Low ≤ 0°F
Jan 0.0 17.2 28.5 5.8
Feb 0.0 11.7 24.0 2.6
Mar 0.0 3.7 20.4 0.1
Apr 0.0 0.1 7.5 0.0
May 0.8 0.0 0.6 0.0
Jun 3.8 0.0 0.0 0.0
Jul 7.2 0.0 0.0 0.0
Aug 4.3 0.0 0.0 0.0
Sep 1.7 0.0 0.2 0.0
Oct 0.0 0.0 4.5 0.0
Nov 0.0 2.1 16.1 0.0
Dec 0.0 10.9 26.6 2.4
         
Annual 17.8 45.6 128.5 10.8
Winter 0.0 39.8 79.0 10.7
Spring 0.8 3.8 28.6 0.1
Summer 15.3 0.0 0.0 0.0
Fall 1.7 2.1 20.9 0.0

Snowfall Summary

Station: 111549 CHICAGO OHARE AP, IL

1971-2000 Averages

Element Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann
Snow (in) 11.3 8.3 6.0 1.6 0.0 0.0 0.0 0.0 0.0 0.3 1.8 8.7 38.0

Snowfall Extremes

Period of Record: 1958-2006

Month High (in) Year 1-Day Max (in) Date
Jan 34.3 1979 18.6 01-02-1999
Feb 26.2 1994 11.1 02-18-2000
Mar 24.7 1965 8.5 03-21-1992
Apr 11.1 1975 10.7 04-02-1975
May 1.6 1966 1.6 05-11-1966
Jun 0.0 - - -
Jul 0.0 - - -
Aug 0.0 - - -
Sep 0.0 - - -
Oct 6.6 1967 4.0 10-27-1967
Nov 10.4 1959 5.0 11-26-1975
Dec 35.3 1978 10.1 12-31-1978
Season (Jul-Jun) 83.7 1978-1979 18.6 01-02-1999

Snowfall Threshold Climatology

Derived from 1971-2000 Averages

*Annual values may differ from the sum of the monthly values due to rounding.


Month 		# Days
Total ≥ 0.1" 		# Days
Total ≥ 1.0" 		# Days
Total ≥ 2.0" 		# Days
Total ≥ 5.0"
Jan 6.6 2.8 1.5 0.3
Feb 6.6 2.8 1.5 0.3
Mar 4.6 2.0 0.9 0.2
Apr 1.2 0.3 0.2 0.1
May 0.0 0.0 0.0 0.0
Jun 0.0 0.0 0.0 0.0
Jul 0.0 0.0 0.0 0.0
Aug 0.0 0.0 0.0 0.0
Sep 0.0 0.0 0.0 0.0
Oct 0.3 0.1 0.0 0.0
Nov 2.3 0.6 0.4 0.0
Dec 7.1 2.6 1.4 0.3
Annual 30.4 12.1 6.2 1.1

Growing Season Summary

Station: 111549 CHICAGO OHARE AP, IL

Growing Degree Day Averages

Derived from 1971-2000 Data

Base Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann
40 6 17 99 279 601 866 1056 1007 736 402 117 20 5211
45 1 6 55 170 449 716 901 852 586 266 59 9 4075
50 0 1 28 92 307 566 746 697 440 158 27 3 3070
55 0 0 12 46 188 418 591 542 300 81 10 1 2194
60 0 0 4 21 103 280 437 387 181 34 2 0 1454
50** 3 9 60 162 360 561 716 680 458 229 59 10 3312

**Modified Growing Degree Days: Base 50, Ceiling 86.

Growing Season Summary

Derived from 1971-2000 Averages

Date of Last Spring Occurrence Date of First Fall Occurrence
Temp °F Median Early 90% 10% Late Median Early 90% 10% Late
32 4/24 4/05 4/09 5/10 5/26 10/14 9/22 9/30 10/31 11/06
30 4/18 3/26 4/05 5/05 5/09 10/20 9/23 10/02 11/10 11/19
28 4/10 3/24 4/04 4/23 5/09 10/25 9/23 10/10 11/15 11/19
24 4/05 3/13 3/22 4/14 4/22 11/09 10/20 10/26 11/24 12/21
20 3/20 2/22 3/11 4/07 4/10 11/18 10/23 11/04 12/03 12/21
16 3/12 2/07 2/15 4/01 4/09 11/29 11/02 11/11 12/11 12/21

Length of Growing Season (Days)

Derived from 1971-2000 Averages

Temp °F Median Shortest 10% 90% Longest
32 172 138 147 199 215
30 182 162 166 214 226
28 197 167 174 221 228
24 217 197 200 242 280
20 238 207 219 264 283
16 263 222 237 285 296

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Copyright 2007 Illinois State Water Survey
Jim Angel, State Climatologist, jimangel@illinois.edu
Last Modified: September 11, 2007