September 2010 Climate Summary

September 2010 Central and Southeast Illinois Weather Summary

September 2010 picked up where August 2010 left off with warmer than normal temperatures and a contrast between wet western and central Illinois and dry eastern Illinois.

Most locations across central and southeast Illinois averaged between 0.75 and 1.75 degrees above normal for the month.  The warmest readings occurred ahead of a cold front on the 21st in southeast Illinois where Lawrenceville topped out at 98 degrees.

Rainfall continued to show the trend of above normal precipitation across much of central Illinois.  Peoria and Lincoln both ended up between 2 and 2.5 inches above normal for the month, while Springfield finished with 7.94 inches (5.20 inches above normal) which made September 2010 the sixth wettest September in Springfield since 1879.  Almost half of the total fell on September 2nd when Abraham Lincoln Capital Airport measured 3.55 inches of rainfall.

While the west and central portions of the state were soggy, the east continues to be dry.  Paris (1.08 inches), Olney (1.12 inches), and Lawrenceville (1.30 inches) struggled to top an inch of rain for the month.  These amounts were around 2 inches below normal for September.

With the contrast showing up across several months, the precipitation for the year to date also reflects this trend with portions of west-central Illinois 15-20 inches above the normal amount for the first three-quarters of the year and portions of southeast Illinois recording 3-5 inches below normal rainfall during the period.


Here are a few of the more significant weather events to occur across central and southeast Illinois during the month:

September 1st-2nd
Most of central Illinois received rainfall thanks to a slow-moving cold front interacting with a very moist airmass.  A large part of the area picked up 1 to 3 inches of rain, with the heaviest amounts in excess of 4 inches extending across parts of Christian, Shelby, and Moultrie counties.  Further south, our southernmost communities from Clay County eastward to the Indiana border completely missed out on the rains, with less than one quarter of an inch reported.  Some hail up to an inch in diameter occurred in Cass, McLean, and Sangamon Counties.

September 10th-11th
An approaching low pressure system and associated warm front brought widespread light to moderate rain to central Illinois during the night of September 10th into the early morning of the 11th.  Due to a cool/dry northeasterly flow around high pressure centered over the eastern Great Lakes, the precipitation tended to diminish as it moved northeastward toward the high.  As a result, the heaviest rainfall occurred along and southwest of a Springfield / Effingham / Robinson line where amounts in excess of 1 inch were common.  Meanwhile, the rain totals quickly trailed off further northeast, with most areas along and northeast of I-74 picking up less than one quarter of an inch. 

September 19th

A weakening thunderstorm complex moved into Illinois during the evening of the 19th and brought 1.5 to 2.5 inches of rain to areas near and northwest of the Illinois River.


Additional information:
Climate summary for Peoria
Climate summary for Springfield
Climate summary for Lincoln
Climate summary for Urbana/Champaign


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