March rainfall in Illinois caused major flooding

[April 10, 2019]    Significant rain in March led to above normal soil moisture in Illinois and major flooding events on many local streams and rivers, according to Brian Kerschner, spokesperson for the Illinois State Climatologist Office at the University of Illinois’ Illinois State Water Survey.

The preliminary statewide average precipitation for March was 4.16 inches, which is 1.20 inches above the long-term average.

Major and historic flooding on the lower Ohio River Basin in southern Illinois continued into the first week of March, as a result of substantial February rain events.

By the middle of the month, a strong and historic low-pressure system brought heavy rain, storms, and strong wind to Illinois and the rest of the Midwest. The heavy rains and combined regional snow melt resulted in additional widespread flooding concerns across the region. This included a major flooding event for northern and northwest Illinois, with the Rock, Fox, and Mississippi Rivers experiencing significant crests.
 

The heaviest March precipitation fell across the central and southern portions of the state where 4 to 6 inches were common. Five stations in these regions reported over 6 inches of precipitation for the month.

Totals were lower in northern Illinois with generally 1.5 to 3 inches. The lowest totals for the month occurred along the Illinois/Wisconsin border.

The highest March precipitation total of 6.41 inches was reported at a station near Jerseyville in Jersey County.

Soil moisture profiles across Illinois remain in the 90th percentile or higher heading into April. This leaves soil conditions favorable for spring runoff, an ever-growing concern for the agricultural community.

Low temperatures began the first full week of March with a brutal Arctic outbreak in which temperature departures of 15 to 25 degrees below normal were common across Illinois.

During this time, three stations recorded minimum temperatures of -10 degrees or colder. The lowest reading in the state, -12 degrees, occurred at the Little Red School House station in Cook County on March 5.

In contrast, the warmest reading in the state was 76 degrees, reported at a station near Dixon Springs in Pope County on March 13.

Preliminary results show that March 2019 finished with a statewide average temperature of 36.6 degrees, which is 4.7 degrees below the long-term average.

March temperature departures finished below average statewide, with the coldest departures occurring across large areas of central Illinois and in the northwest corner of the state.

Snowfall in March occurred statewide, although it rarely lasted long. Storm tracks show that the maximum snowfall was near the corridor from Rushville to Springfield, and a second was centered near Kankakee. In both cases, 3 to 5 inches of accumulation were measured.

The National Weather Service (NWS) spring flood outlook places the entire state in its flood risk zone. Eastern and central Illinois are subject to a minor flood risk, while western, extreme northern, and southern portions of the state are in a moderate flood risk zone. Locations immediately along the banks of the Mississippi River are in a major flood risk zone.

Looking ahead at the rest of April 2019, the Climate Prediction Center (CPC) is favoring probabilities of above average temperatures statewide. This is a welcome change compared to April 2018, which ranked as the second coldest April in state history. An active weather pattern looks to persist, as the April outlook favors slight probabilities of above average precipitation for the western half of the state.

[Lisa Sheppard]