Based on preliminary data, Illinois experienced above-normal temperatures and rainfall for September in Illinois. Here are the statistics for the state:
- The statewide average temperatures for September was 70.0 degrees, 3.8 degrees above normal and the 12th warmest September on record. We were on track to one of the warmest Septembers on record until the last cold snap.
- The statewide average rainfall for September was 4.97″, 1.74″ above normal and the 19th wettest September on record.
- The hottest temperature recorded for September was 99 degrees at Springfield Airport on September 5.
- The coldest temperature recorded for September was 30 degrees at Ottawa on September 29.
- The highest monthly rainfall total for September was 12.43″ at Clay City (just south of Effingham).
Here are the rainfall totals (left) and departures from normal (right) for September in Illinois (click to enlarge). Rainfall was heaviest in southern Illinois with amounts up to 12 inches and in northwestern and western Illinois with amounts up to 10 inches – all well above normal. There was a band of drier conditions stretching from St. Louis to Chicago where rainfall totals of 1 to 3 inches were common.
In addition, heavy rains fell across the upper Midwest in September (maps below, click to enlarge). The rains were especially heavy in Wisconsin, Iowa, and Minnesota, leading to river flooding in Illinois along the Mississippi and rivers coming out of Wisconsin
Temperatures across the Midwest were much above normal in September (map below with pumpkin spice-colored shading – appropriate for this time of year). While Illinois was 3.8 degrees above normal, Indiana was 4.5 degrees above normal, Kentucky was 5.0 degrees above normal, and Ohio was 5.5 degrees above normal. The other states were 1 to 3 degrees above normal for the month.
Outlook for October
Finally, here is the outlook for October that was released by the NWS on September 30. These rely heavily on the more reliable forecasts out to 14 days. Those forecasts show Illinois with very strong chances for above-normal temperatures and rainfall. As a result, the October outlook also shows most of Illinois with an increased chance of above-normal temperatures and all of Illinois with an increased chance of above-normal temperatures.
On a side note, the 4-corners region (UT, CO, AZ, and NM) are in a severe drought and the expected rainfall will be welcomed there. The same cannot be said for the Upper Midwest, which was already very wet in September.
See the page on normals for more on this topic.