National Weather Service Weather Forecast Office

Temperatures across cenntral and southeast Illinois were generally at or 1 to 2 degrees below 
the 30 year average temperature. (see graphic below) The monthly average temperatures were 
27.3 degrees (2 degrees below normal) in Lincoln, 27.8 degrees (right at the 30 year normal 
temperature) in Peoria and 30.2 degrees (0.1 drees below normal) in Springfield. Precipitation, 
on the other hand, was 1 to 3 inches above the 30 year average. (see graphic below) In fact, Dec 
2009 was the 6th wettest on record in Peoria (with 4.17 inches), and the 9th wettest in Springfield
(with 4.45 inches).

December 2009 Departure from normal temperatures. Image from the IL State Climatologist office and Midwest Regional Climate Center	December 2009 Departure from normal precipitation. Image from the IL State Climatologist office and Midwest Regional Climate Center

December 2009 was an active month across central and southeast Illinois. There were 2
major storm systems to affect the area. The first system occurred on December 8th and 9th.
A weak cold front moved into western Illinois on December 7th...then a strong low pressure
system tracked northeast along the front (just west of the Illinois River) December 8th and
9th. Heavy snow was noted across Knox County...with snowfall amounts of 6 to 7 inches reported.
Very strong winds occurred behind the departing low on December 9th. Very cold air poured into
the area behind this system. The coldest temperratures observed were 0 degrees on Dec 10th in
Galesburg and Knoxville.
For more information on the December 8th and 9th storm, visit:
NWS Lincoln SWOP Event Summary 
IL State Climatologist Summary

The next major storm system of the month was the result of a very slow moving low pressure system,
that meandered northward across the Mississippi Valley. Precipitation began as rain, with a bit
of freezing rain in the north, on the evening of the 22nd and the morning of the 23rd. Warm moist
air was drawn into the system and the precipitation fell as mostly rain, until much colder air
wrapped around the system and changed the precipitation over to snow on Christmas Day. (Daily 
snowfall images from Christmas through December 27 can be found below.0 Much colder
air poured in behind this departing system, and some of the colder morning low temperatures on
Dec 29 were -4 degrees in Altona, -1 near Congerville, 0 degrees in Minonk and 1 degree at the NWS
in Lincoln.
For more information on the December 22 to 27, visit:
NWS Lincoln SWOP Event Summary

The precipitation that occurred from December 23 through the 27th, resulted in minor flooding of
central Illinois Rivers. Moderate flooding occurred on the Illinois River at Havana and Beardstown,
and along the Mackinaw River near Congerville. The Illinois River crested on New Years Day at 19.05
feet (5.05 feet above flood stage) in Havana, and 21.02 feet (7.02 feet above flood stage0 in
Beardstown.