The preliminary average statewide September temperature was 71.3
degrees, which is 4.9 degrees above the long-term average.
Monthly temperature departures ranged from 2 to 4 degrees warmer
than normal in northeast Illinois to over 6 degrees warmer than
normal in southwest Illinois.
September average temperatures across the state ranged from 65
degrees in Jo Daviess County to 78 degrees in Lawrence County.
The lowest minimum temperature reported in Illinois was 45
degrees in Jo Daviess County on Sept. 5, and the highest maximum
temperature was 97 degrees in both Alexander and Pope Counties
on Sept. 16.
Well over 100 local daily climate records were broken in
Illinois in September, most of which were high daily minimum
temperature records. These conditions were attributed to several
very warm nights, including the night of Sept. 22, when the
nighttime minimum temperature remained above 70 degrees as far
north as Elizabeth in Jo Daviess County and Freeport in
On the night of Sept. 10, the station in Rock Island reported a
nighttime minimum temperature of 77 degrees, besting the
previous daily record by 3 degrees.
Precipitation in Illinois varied tremendously from north to
south across the state. The preliminary average statewide
precipitation was 5.34 inches, which is 1.9 inches above the
long-term September average. However, the data also show large
differences in September precipitation totals across the state,
with northern Illinois receiving much more than average
precipitation, and southern Illinois receiving much less than
Areas of northern and north-central Illinois received in excess
of 12 inches of rainfall in September, while areas of southeast
Illinois received less than 0.25 inches over the same time
Locally, a station near Stockton in Jo Daviess County observed
16.62 inches in September, or nearly 13 inches more than normal,
while the station at Smithland Lock & Dam in Pope County
recorded only 0.02 inches, or 3.5 inches less than normal.
The latest U.S. Drought Monitor Sept. 24 map shows a pocket of
moderate drought covering parts of Champaign, Ford, Iroquois,
and Vermilion counties. Concurrently, below normal rainfall and
above normal temperatures in the southern part of the state
generated abnormally dry conditions in September.
The latest U.S. Drought Monitor depicts abnormally dry
conditions for most of Illinois south of I-64, and a pocket of
moderate drought from Pope and Hardin counties in the southeast
to Perry and Franklin counties in south-central Illinois.
Conditions in southern Illinois have shown some signs of a flash
drought, which is a rapidly intensifying drought event, often
provoked by an existing precipitation deficit combined with
[to top of second column]
Reports from Illinois Farm Bureau CropWatchers
regarding drought in east-central and southern Illinois are mixed.
Some report the dryness and heat have helped late-planted crops
reach maturity, while at the same time possibly sacrificing yield.
In contrast to the ongoing drought in southern and east-central
Illinois, September was abnormally wet for most of northern and
north-central Illinois. Persistent, heavy rains led to flooding
impacts in parts of northern Illinois, including the closure of
several state parks and significant flooding along the Fox and Des
Plaines Rivers, among others.
Areas in northern and north-central Illinois received in excess of
12 inches of rainfall in September. In most parts of Peoria,
Woodford, Marshall, and Livingston counties, most of the rainfall
totals came in a 24-hour period between Sept. 27 and 28. This event
created dangerous flash flooding from Peoria into the southwest
The COOP station in Minonk in Woodford County recorded 9.09 inches
of rainfall over that 24-hour period, although that likely fell over
a less than 12-hour window. This total approached the 24-hour,
500-year storm total of 9.53 inches and surpassed the 12-hour,
500-year storm total of 8.29 inches.
A 500-year storm total refers to a precipitation accumulation over a
given time period (e.g., 12, 24, 48 hours, etc.) and has a 0.2
percent chance of occurring in a given year.
The 9.09-inch total in Minonk broke, and nearly doubled, the
all-time 24-hour precipitation total record at that station, which
was just over 5 inches (data going back to 1895). Images of flooded
fields in Woodford and Marshall Counties suggest this most recent
heavy precipitation event may delay harvest.
Short-term temperature forecasts call for continued above average
temperatures for the first few days of October and then a regression
to cooler, more seasonal conditions. Longer term Climate Forecast
System (CFS) forecasts from the National Centers for Environmental
Protection show probabilities of a 32-degree freeze in Illinois
remain below 30 percent into the third week of October.
Looking into October, the 8 to 14-day outlook from the Climate
Prediction Center (CPC) shows elevated probabilities of above normal
temperatures and elevated probabilities of above normal
precipitation across the state. The CPC monthly outlook for October
still shows elevated probabilities for below normal temperatures
across the northern half of the state, with equal chances (above
normal, normal, below normal precipitation) for all but the very
northwest corner of Illinois.