Chicago, IL

Weather Forecast Office

Spring Flood Outlook for Northeast Illinois and Northwest Indiana

Outlook Valid
Spring 2021

Last Updated
March 11, 2021

Based on current conditions, the risk of flooding ranges from below average to near average.

The spring flood outlook is updated each February and March. Next scheduled update Spring 2022.

Risk Factors for Spring Flooding

To determine the relative risk of spring flooding, numerous factors are considered including snow cover, soil moisture, and current river conditions. A significant snow cover with high water content can increase the chances of flooding once warmer weather melts the snow. Elevated soil moisture conditions reduce the amount of rainfall that is soaked up by the ground and increase the amount of water that then runs off into area streams. Above average river levels reduce the river rise required to reach flood stage, while below average river levels would require an increased amount of river rise to reach flood stage.

Spring Flood Outlook 2021

Winter 2020-2021 Review

Fall 2020 Review

Spring Flood Risk Factors

Here is a general overview of spring flood risk factors across northeast Illinois and northwest Indiana river basins.

Risk Factor	Current Condition	Effect on Flood Risk
Fall/Winter River Levels	Below Average to Above Average	Decrease/Increase
Fall/Winter Soil Moisture	Below Average to Above Average	Decrease/Increase
Winter Precipitation (Snow Cover)	Near Average	No effect/Increase
Winter Temperatures (Frost Depth)	Near Average	No effect/Decrease
Spring Precipitation	Unknown	-
Spring Temperatures (Snow Melt)	Near to above average temperatures, all snow melted	No effect/Decrease

Valid March 11, 2021.

Current Snow Cover and Snow Water Equivalent

Modeled snow cover (below, left) across area river basins is at 0 inches across the area, which contains 0 inches of water equivalent (below, right). All snow cover has melted since the previous outlook.

Valid March 11, 2021. Click here for the latest snow cover information.

Current Soil Moisture and Frost Depth

Modeled soil moisture values (below) across the area range from below average to near average. Values are the lowest in northern Indiana, at the 5^th to 10^th percentile for this time of year.

Frost depth ranges from 0 to 10 inches across area river basins, with the deepest frost depth values reported in isolated parts of southern Wisconsin. The majority of locations have no frozen soil. Despite very cold weather in February, the heavy snow pack has reduced the frost depth penetration.

Valid March 11, 2021. Click here for the latest soil moisture information from the Climate Prediction Center.

Current River Conditions

River streamflow across the area ranges from much below average to much above average (below). The highest streamflow levels are in southern Wisconsin and northern Illinois.

River ice spotters report generally ice-free rivers across the area. Although March can sometimes experience temperatures favorable for the formation of river ice, the risk of additional heavy ice cover and ice jams is low as of this outlook.

Valid March 11, 2021. Click here for the latest streamflow conditions from the USGS. Click here for the latest river ice spotter reports.

Spring Weather Outlook

The long term (next couple months) outlook from the Climate Prediction Center indicates generally near average temperatures favored by late-March, with near average temperatures favored for the remainder of spring. The outlook indicates above average precipitation slightly favored for spring.

Although snow cover, soil moisture, and recent river levels can provide some indication of the relative risk of spring flooding, any weather system that produces heavy rainfall could cause flooding. Spring flood outlooks are not able to assess the risk of flooding due to heavy rainfall more than a week or so in advance.

Detailed Flood Outlook

Click here for the detailed Spring Flood Outlook which includes tables with probabilities of flooding along area rivers. Relative flood risk can also be viewed on the Advanced Hydrologic Prediction Service (AHPS) page for our area.

Temperature

Temperatures for winter 2020-2021 averaged about 2F below to 1F above the climatic average in northeast Illinois and northwest Indiana. There was a large range in winter temperatures across the season, with December and January generally above average and temperatures for early February below average.

Precipitation

Precipitation for winter 2020-2021 averaged 2 inches below to 2 inches above the climatic average in northeast Illinois and northwest Indiana.

Snowfall

The first measurable snowfall (>0.1 inches) across northeast Illinois (right) occurred in either mid-October or late November. The first measurable snow in northwest Indiana generally occurred in late November to early December.

As of March 11, 2021, the season-to-date snowfall ranged from 20 to 50 inches across the area, with the highest totals (over 30 inches) in northwest Illinois and southern Wisconsin, and also along the immediate shore of Lake Michigan. Observed snowfall ranged from slightly above the climatic average in central Illinois to about 20 inches above average in northwest Illinois (right, below).

River ice conditions in December and January caused a few minor ice jams but caused no flooding. Very cold weather in early February caused heavy ice cover, but few ice jams.

Temperature

Temperatures were generally near the climatic average across northeast Illinois and northwest Indiana during fall 2020. Almost all areas experienced temperatures within 1F of average.

Precipitation

Precipitation ranged from below average in northwest Indiana to above average in northern Illinois during fall 2020. Precipitation was heaviest to the northwest near the Illinois/Wisconsin/Iowa border. Portions of northwest Indiana experienced precipitation about 75% of average, while precipitation to the far northwest experienced precipitation 125-150% of average.