National Weather Service United States Department of Commerce

Outlook Valid
Spring 2021

Last Updated
February 25, 2021


Based on current conditions, the risk of flooding ranges from below average to above average. The greatest risk of flooding is in the Rock, Fox, and Des Plaines River basins.

 

The spring flood outlook is updated each February and March. Next scheduled update March 11th.

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 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
(through Feb 24)
No effect/Increase
Winter Temperatures (Frost Depth) Near Average
(through Feb 24)
No effect/Decrease
Spring Precipitation Unknown -
Spring Temperatures (Snow Melt) Unknown -


Valid February 25, 2021.

 

Current Snow Cover and Snow Water Equivalent

 

Modeled snow cover (below, left) across area river basins ranges from near 2 inches to near 18 inches, which contains 0.25 inches to 4 inches of water equivalent (below, right). The deepest snow cover was in far northwest Illinois and southwest Wisconsin. The majority of the area had snow water equivalent values of 1.5-3.0 inches.

Current Modeled Snow DepthCurrent snow water equivalent

Valid February 23, 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 slightly below average to slightly above average. Values were the lowest in northern Indiana, at the 10th to 20th percentile for this time of year. Values were highest in southern Wisconsin, at the 80th to 90th percentile.

Frost depth ranged from 4 to 10 inches across area river basins, with the deepest frost depth values reported in southern Wisconsin. Despite very cold weather, heavy snow pack has reduced the frost depth penetration.

Valid February 23, 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 above average (below). The highest streamflow levels are in southern Wisconsin and northern Illinois.

USGS streamflow conditions for the United States

River ice spotters report generally ice-covered rivers across the area. The most significant river ice cover is likely occurring in the Rock and Fox River Basins. Heavy river ice may lead to ice jams this spring, especially if temperatures and precipitation lead to significant river rises, but confidence in exact timing and extent of possible ice jams is low as of this outlook.

Valid February 23, 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 above average temperatures favored by mid-March, with above average temperatures slightly 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 through mid-February averaged about 0-2F below 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.

December January February Temperature Anomaly

Precipitation
 

Precipitation for winter 2020-2021 through mid-February averaged about 0-1 inches above the climatic average in northeast Illinois and northwest Indiana.

December January February Precipitation Anomaly

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 February 24, 2021, the season-to-date snowfall (right, below) ranged from 20 to 45 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.

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.

Winter 2018/2019 first snowfallObserved season-to-date snowfall anomaly

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.

September October November Temperature Anomaly

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.

September October November Precipitation Anomaly