Above-average rainfall continued in June, along with an elevated risk of flooding in some areas of Illinois, according to Brian Kerschner, a spokesperson for the Illinois State Climatologist Office at the Illinois State Water Survey, part of the Prairie Research Institute at Illinois.
The preliminary average statewide precipitation for June was 5.39 inches, or 1.18 inches above the long-term average. A gauge near Cobden in Union County reported the highest official precipitation total for June with 10.73 inches.
June rainfall in Illinois was not evenly distributed. Several regions in the northern half of the state reported precipitation totals slightly below to near average for the month, with localized regions of above-average precipitation. Most of the southern half of the state experienced more uniform above-average precipitation departures, with numerous localities receiving 200% to 300% of normal.
After near-historic crests at multiple gauges along both the Illinois and Mississippi rivers early in the month, water levels continued to slowly recede for many regions heading into July. However, above-average precipitation in June, combined with calculated soil moisture content remaining in the 90th to 99th percentile across Illinois, leaves the state with an elevated risk of continued flooding over the next month, especially in regions that may be affected by storms or locally heavy rainfall.
Flooding concerns along Lake Michigan were common in June. According to the U.S. Army Corps of Engineers, water levels in the Lake Michigan-Huron system have risen by nearly 5 inches throughout the month.
By the end of June, average water levels in the Lake Michigan-Huron system were reported to be 33 inches, or about 2.75 feet above the historical June average. These levels set a new June record by nearly 2 inches. Water levels of this magnitude haven’t been exceeded since 1986.
This also marks the eighth consecutive month in which no part of Illinois has been listed by the U.S. Drought Monitor as in drought or abnormally dry and the seventh consecutive month with above-average statewide precipitation.
The preliminary average statewide June temperature was 71.0 degrees, which is 0.9 degrees below the long-term average.
The middle of the month was characterized by an extended period of unseasonably cool temperatures, while the start of astronomical summer brought a steady warming trend as temperatures reached into the upper 80s and 90s for the final days of June.
Temperature departures for the month were about 1 to 3 degrees below average, with average temperature values ranging from the mid-60s to the mid-70s. The highest maximum temperature recorded in the state at two separate stations was 97 degrees, at a station near Bentley in Hancock County on June 5 and at a station near Flora in Clay County on June 30.
The lowest minimum temperature of 43 degrees was reported in Danville in Vermilion County on the morning of June 14.
Heading into July, the monthly outlook from the Climate Prediction Center favors slight probabilities for below-average temperatures across most of the state, as well as continued probabilities of wetter-than-average conditions statewide.