National Weather Service Weather Forecast Office

Canadian airmasses repeatedly invaded the Midwest during the summer of 2009.  The jet stream pattern allowed much below normal temperatures to persist across central and southeast Illinois for much of July and August.  Many locations saw average mean temperatures for meteorological summer (June through August) of 1 to 3 degrees below normal, which put many sites in their top 10 coolest summers on record. 

Below is a listing of how summer 2009 ranked in relation to the top 5 coolest summers for several cities.

Bloomington/Normal (records date to 1893)
(1) 69.1 - 1992
(2) 69.6 - 2009
(3) 69.9 - 1915
(4) 70.0 - 1927
(5) 70.8 - 1924

Charleston (records date to 1896)
(1) 69.5 - 1915
(2) 70.8 - 1927
(3) 71.4 - 1958
(4) 71.6 - 1982
(5) 71.7 - 1992
(19) 73.3 - 2009

Decatur (records date to 1893)
(1) 70.7 - 1927
(2) 70.9 - 1915
(3) 71.4 - 1992+
(4) 71.7 - 1982
(5) 71.8 - 1904+
(17) 73.5 - 2009+

Flora 5NW (records date to 1893)
(1) 71.3 - 1927
(2) 71.7 - 1904
(3) 72.3 - 1915
(4) 72.5 - 1982
(5) 72.6 - 1903
(7) 73.1 - 2009+

Galesburg (records date to 1895)
(1) 68.0 - 1904
(2) 69.0 - 1992
(3) 69.4 - 2009+
(4) 69.8 - 1908
(5) 70.1 - 1967

Lincoln (records date to 1905)
(1) 69.8 - 1927
(2) 69.9 - 2004
(3) 70.3 - 2009
(4) 70.7 - 1915
(5) 71.1 - 1967

Peoria (records date to 1883)
(1) 69.0 - 1915
(2) 69.8 - 1927
(3) 70.2 - 2004+
(4) 70.4 - 1950
(5) 70.8 - 1985+
(7) 71.1 - 2009

Springfield (records date to 1879)
(1) 70.4 - 2004
(2) 70.7 - 1915
(3) 70.8 - 1950
(4) 71.4 - 1927+
(5) 71.6 - 1992+
(10) 72.4 - 2009+

Urbana (records date to 1888)
(1) 68.7 - 1889
(2) 68.9 - 1915
(3) 69.1 - 1927
(4) 70.1 - 1992
(5) 70.2 - 2004
(9) 70.9 - 2009+

Below are some temperature maps courtesy of NOAA MRCC.