After the extremely low rainfall that occurred during the spring and summer months, September was unusually wet for eastern and southeast Illinois. The first image below shows rainfall for the month of September. Amounts of 6 inches or more are indicated in the red shades over much of east central Illinois, while pink areas of far southeast Illinois received in excess of a foot of rain during September! Some of the highest totals were reported in Clay County, where specific amounts include 14.37" near Clay City, and 14.20" at Flora. In Olney (Richland County), 9.64" fell this month. However, such high amounts did not occur over the entire area. Farther northwest, the western portions of central Illinois only received near normal to slightly below normal rain as shown in the second image. In fact, the Springfield's Capital Airport ended up 0.01" below normal for the month with only 2.89".
The above normal rainfall for much of the region was caused by two factors: (1) The remnants of Hurricane Isaac which impacted the area Aug. 31 through Sept. 3, and (2) a return to an active storm track which brought several rounds of moderate to heavy rains to the southeast third of Illinois. As a result, drought conditions eased. Before the rains of Isaac most of the area was in severe to extreme drought. But by the end of the month the extreme drought conditions had disappeared and severe drought was confined to several counties northwest of Lincoln, including the Peoria and Galesburg areas. Farther southeast where most of the beneficial rains fell (2 to 3 times normal), the drought had eased to moderate or even just abnormally dry by late month. The maps below from the U.S. Drought Monitor indicate observed drought conditions across the state on August 21 (top image), and September 25 (bottom image). Note how the red shading (extreme drought) has shrunk.
Severe weather was limited during the month. Several weak tornadoes developed on Saturday, September 1, when the remnants of Hurricane Isaac moved north into the area. These tornadoes touched down north of Peoria, in rural portions of Stark, Marshall, and Woodford counties.
Other severe weather events occurred on September 5, 7, and 21, when scattered thunderstorms produced hail and isolated damaging winds.
Temperatures across the region averaged 1 to 3 degrees below normal for the month. This was the second month in a row of below normal temperatures, after January through July all recorded above normal temperatures. Only one daily record was set: Springfield tied a record low of 33 degrees on September 24. Lincoln recorded their 9th coldest September on record.