Some areas of Illinois experienced record-breaking amounts of rain in May, as statewide totals mark the sixth consecutive month with above average rainfall, 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 in May was 8.43 inches, which is 3.83 inches above the long-term average. As it stands now, spring 2019 will rank within the top four wettest spring seasons in state history (March-May), with May 2019 ranking as the third-wettest May in state history.
The preliminary average statewide temperature for May was 62.5 degrees, which is 0.2 degrees below the long-term average.
Almost the entire state received above-average precipitation for the month. The only exception was a small region in east-central Illinois near Edgar County, where near- to slightly below-average precipitation occurred.
Portions of west-central and northern Illinois reported the heaviest rainfall for the month, where monthly precipitation departures of 5 to 8 inches above average were common, bringing 200% to 300% of average monthly rainfall. An area roughly defined between Quincy and the Quad Cities extending eastward to near Peoria received the most precipitation in the state, with 7 rain gauges in this region recording 13 or more inches of rainfall during May.
A gauge near Dallas City in Hancock County reported the highest precipitation total for May with 14.75 inches.
Data from the National Weather Service showed that with a report of 8.25 inches, Chicago experienced its wettest May on record, beating the 8.21-inch reading that was set just last year.
The abnormally wet May weather has led to a continuation of elevated flooding risks and significant planting delays for the Illinois agricultural community. Moderate and major flooding along many local streams and rivers is still ongoing, with flood warnings along both the Illinois and Mississippi rivers in effect until further notice.
Wet, active and stormy weather has not only been an issue for Illinois but also has been a growing risk across much of the central and southern Midwest, where notable above-average precipitation departures for May were also present.
In addition to the relentless rainfall, multiple rounds of severe weather affected the state throughout the month. Statewide, 215 severe weather reports were noted – 18 for tornadoes, 51 for hail and 146 for wind. Note that multiple reports may be generated for a single event.
Monthly temperature departures showed that the northern third of the state generally saw average temperatures of 1 to 3 degrees below normal, while the southern third of the state generally saw average temperatures of 1 to 3 degrees above normal, with near-normal temperatures occurring throughout central Illinois.
The highest maximum temperature in the state was recorded at the Kaskaskia River Navigation Lock in Randolph County with a reading of 93 degrees on May 26. In contrast, the lowest minimum temperature of 31 degrees was recorded at the Chicago Botanical Garden on May 4.
Although an active weather pattern looks to continue at least for a portion of the first full week of June, the monthly outlook from the Climate Prediction Center favors equal probabilities for below, near or above average precipitation and temperatures across Illinois for June.