Heavy rains forecast for northern Illinois on Monday, prompting flooding advisory

Heavy rains starting Monday could cause localized flooding in parts of northern Illinois from areas extending eastward from Lee and Ogle counties, the National Weather Service said in an advisory issued Saturday.

The rain in some areas may be “high enough to cause river rises, widespread ponding of water, and localized flooding,” the advisory read.

The range of the advisory zone extends from Illinois’ border with Wisconsin, east into parts of Indiana and Michigan, and as far south as Illinois’ Ford and Vermilion counties.

The first heavy rains are expected on Monday, the weather service said.

The forecast for across the advisory zone largely calls for light rain and winds increasing to 25 mph Sunday evening, with thunderstorms arriving sometime after midnight through early morning Monday.

Dixon, which is on the westernmost edge of the advisory zone, is expected to see the heaviest downpours around 3 a.m.

Rainfall amounts between a one-half and three-quarters of an inch are possible. More rain and winds — gusts up to 45 mph are expected.

The service said the heavy rain and already saturated soil could cause river levels to rise above the banks for the Fox, Des Plaines, Rock and Kankakee river basins.

Even a limited amount of rain could cause the water in the already-elevated Iroquois and Illinois river basins to rise above their banks.

Rainfall amounts between a one-half and three-quarters of an inch are possible. More rain and winds — gusts up to 45 mph are expected.

—  

The service also forecast strong winds ranging from 35 to 40 knots across Iowa and northern and central Illinois. These winds are centered on a line along the Interstate 80 corridor from Des Moines, Iowa, to La Salle, but extending north to about Sterling and south to Macomb and Peoria.

The advisory comes a day after the service revised its spring flood risk assessments to show increasing risk of flooding. The Quad Cities Hydrologic Service Area outlook showed “above normal” flood risk for the Mississippi River and “near normal” flood risk for local tributaries.

The reason for the revision was above average snowpack for the northern reaches of the Mississippi River basin and  precipitation in the last two weeks that caused stream flows in the watershed to be above normal.

The service’s Chicago station issued a report on the ice storm of Wednesday and Thursday. Rockford Airport saw an ice accretion of 0.37 inches, but Timberlane, Harvard and Winnebago all saw 0.30 inches. Cissna Park recorded 3.71 inches of rain while Romeoville got 1.09 inches.