Historical Climate Data

Precipitation Summary

Station: 117382 ROCKFORD AIRPORT, IL

1971-2000 NCDC Normals

Element Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann
Prec. (in) 1.41 1.34 2.39 3.62 4.03 4.80 4.10 4.21 3.47 2.57 2.63 2.06 36.63

Precipitation Extremes

Period of Record: 1951-2006


Month
High (in)
Year
Low (in)
Year 		1-Day
Max (in)
Date
Jan 4.66 1960 0.18 1961 2.46 01-12-1960
Feb 3.05 2001 0.04 1969 1.65 02-09-1966
Mar 5.62 1961 0.43 2005 2.50 03-04-1976
Apr 9.92 1973 0.99 1989 3.38 04-21-1973
May 11.75 1996 0.48 1992 4.77 05-28-1996
Jun 11.85 1993 0.46 1988 3.94 06-14-1972
Jul 11.81 1952 0.75 2001 4.99 07-08-1951
Aug 13.55 1987 0.48 2003 5.70 08-14-1987
Sep 10.68 1961 0.05 1979 5.56 09-13-1961
Oct 8.32 1969 0.01 1952 4.78 10-10-1954
Nov 5.51 1985 0.38 1976 2.09 11-16-1961
Dec 5.04 1971 0.37 1955 2.00 12-02-1982
             
Annual 56.48 1973 23.25 1976 5.70 08-14-1987
Winter 9.19 1960 1.28 2003 2.46 01-12-1960
Spring 21.43 1973 3.92 2005 4.77 05-28-1996
Summer 25.76 1972 4.81 1988 5.70 08-14-1987
Fall 21.56 1961 3.05 1956 5.56 09-13-1961

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 10.1 3.9 0.6 0.1
Feb 8.5 3.6 0.7 0.1
Mar 10.9 5.2 1.4 0.4
Apr 11.8 6.5 2.5 0.7
May 12.0 6.8 2.5 1.2
Jun 10.1 7.1 3.3 1.3
Jul 9.7 6.5 2.6 1.2
Aug 9.9 7.0 2.9 1.1
Sep 8.8 5.4 2.5 0.9
Oct 9.2 4.9 1.5 0.5
Nov 10.5 5.3 1.9 0.5
Dec 10.5 4.9 1.2 0.3
         
Annual 122.0 67.1 23.4 8.2
Winter 29.2 12.4 2.5 0.5
Spring 34.7 18.5 6.4 2.3
Summer 29.7 20.6 8.8 3.6
Fall 28.4 15.6 5.8 1.9

Temperature Summary

Station 117382 ROCKFORD AIRPORT, IL

1971-2000 NCDC Normals

Element Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann
High °F 27.2 33.0 45.5 59.1 71.2 79.9 83.1 80.9 73.9 61.8 45.5 32.0 57.8
Low °F 10.8 16.3 26.7 36.8 47.9 57.6 62.6 60.9 51.8 40.1 29.0 16.9 38.1
Mean °F 19.0 24.7 36.1 47.9 59.6 68.8 72.9 70.9 62.8 51.0 37.2 24.4 47.9
HDD 1430 1143 912 522 215 36 5 14 136 444 832 1244 6933
CDD 0 0 1 7 49 162 263 205 74 7 0 0 768

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

Temperature Extremes

Period of Record: 1951-2006


Month 		High
Mean °F
Year 		Low
Mean °F
Year 		1-Day
Max °F
Date 		1-Day
Min °F
Date
Jan 33.5 2006 5.9 1977 63 01-31-1989 -27 01-10-1982
Feb 36.6 1998 12.3 1978 70 02-25-2000 -24 02-03-1996
Mar 43.0 2000 22.5 1960 85 03-29-1986 -11 03-01-1962
Apr 55.1 1977 42.5 1975 91 04-22-1980 5 04-07-1982
May 68.2 1977 51.4 1966 95 05-19-1975 24 05-10-1966
Jun 74.3 2005 63.6 1969 101 06-20-1988 37 06-01-1993
Jul 79.5 1955 69.1 1996 103 07-27-1955 43 07-05-1967
Aug 77.2 1983 65.6 1992 104 08-16-1988 41 08-25-1958
Sep 68.4 2005 58.0 1975 102 09-01-1953 27 09-30-1984
Oct 62.0 1963 44.7 1987 90 10-06-1963 15 10-29-1952
Nov 47.6 2001 28.1 1976 76 11-02-1961 -10 11-26-1977
Dec 33.1 1982 12.6 2000 67 12-05-2001 -24 12-24-1983
                 
Annual 51.6 1998 45.4 1979 104 08-16-1988 -27 01-10-1982
Winter 30.9 2002 14.2 1979 70 02-25-1900 -27 01-10-1982
Spring 55.2 1977 43.4 1960 95 05-19-1975 -11 03-01-1962
Summer 75.3 1983 67.4 1992 104 08-16-1988 37 06-01-1993
Fall 56.5 1963 44.4 1976 102 09-01-1953 -10 11-26-1977

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 19.6 29.6 8.3
Feb 0.0 13.3 25.5 4.6
Mar 0.0 4.4 22.4 0.3
Apr 0.1 0.2 9.1 0.0
May 0.5 0.0 0.9 0.0
Jun 3.4 0.0 0.0 0.0
Jul 5.6 0.0 0.0 0.0
Aug 3.4 0.0 0.0 0.0
Sep 1.1 0.0 0.6 0.0
Oct 0.1 0.0 7.0 0.0
Nov 0.0 3.4 19.7 0.2
Dec 0.0 14.2 28.2 4.1
         
Annual 14.3 55.1 143.1 17.5
Winter 0.0 47.1 83.3 17.0
Spring 0.6 4.6 32.4 0.3
Summer 12.5 0.0 0.0 0.0
Fall 1.2 3.4 27.4 0.2

Snowfall Summary

Station: 117382 ROCKFORD AIRPORT, IL

1971-2000 Averages

Element Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann
Snow (in) 10.3 8.0 5.6 1.4 0.0 0.0 0.0 0.0 0.0 0.1 2.6 10.8 38.8

Snowfall Extremes

Period of Record: 1951-2006

Month High (in) Year 1-Day Max (in) Date
Jan 26.1 1979 9.5 01-13-1979
Feb 30.2 1994 9.6 02-18-2000
Mar 22.7 1964 10.4 03-29-1972
Apr 7.7 1982 6.3 04-05-1982
May 1.0 1966 1.0 05-11-1966
Jun 0.0 - - -
Jul 0.0 - - -
Aug 0.0 - - -
Sep 0.0 - - -
Oct 2.2 1967 1.7 10-26-1967
Nov 14.7 1951 6.6 11-27-1995
Dec 30.1 2000 10.7 12-01-2006
Season (Jul-Jun) 74.5 1978-1979 10.7 12-01-2006

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 6.0 2.4 1.2 0.2
Feb 6.0 2.4 1.2 0.2
Mar 4.7 1.6 1.0 0.2
Apr 1.4 0.4 0.2 0.0
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 0.2 0.0 0.0 0.0
Nov 2.9 0.8 0.4 0.0
Dec 7.5 3.1 1.8 0.5
Annual 32.1 12.0 6.4 1.3

Growing Season Summary

Station: 117382 ROCKFORD AIRPORT, 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 2 9 79 274 617 881 1038 973 696 360 85 11 5031
45 0 2 41 164 464 731 883 818 547 232 41 4 3932
50 0 0 19 86 320 581 728 663 401 133 16 1 2953
55 0 0 7 41 197 431 573 508 265 65 5 0 2098
60 0 0 2 18 107 288 418 355 156 25 0 0 1373
50** 1 6 52 168 379 575 705 651 435 214 47 6 3244

**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 5/01 4/07 4/17 5/12 5/28 10/07 9/12 9/23 10/21 11/04
30 4/24 4/07 4/10 5/11 5/28 10/11 9/23 9/23 10/24 11/05
28 4/12 3/26 4/04 4/27 5/08 10/18 9/25 10/02 11/05 11/17
24 4/07 3/24 3/29 4/19 4/22 11/02 10/04 10/16 11/16 11/19
20 4/01 3/09 3/17 4/11 4/18 11/11 10/19 10/27 11/25 12/07
16 3/20 2/17 2/24 4/07 4/18 11/21 11/02 11/08 12/07 12/21

Length of Growing Season (Days)

Derived from 1971-2000 Averages

Temp °F Median Shortest 10% 90% Longest
32 159 125 138 180 204
30 167 137 141 188 208
28 188 140 167 207 222
24 206 174 188 224 237
20 221 207 209 248 252
16 246 217 223 276 284

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