As we begin to see some actual above-freezing temperatures this week, it’s probably a good idea to take note of the National Weather Service Chicago’s forecast of an “above average” flood risk in Kane County.
According to the NWS-C’s Spring Flood Outlook for Northeast Illinois and Northwest Indiana, based on current conditions, 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, and the next scheduled update is Feb. 25, so we’ll be sure to let you know what the situation is at that time.
To determine the relative risk of spring flooding, numerous factors are considered, including snow cover, soil moisture, and current river conditions.
Snow Cover, Other Factors
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.
Back on Feb. 9, modeled snow cover across area river basins ranged from near 2 inches to near 18 inches, which contains 0.1 inches to 4 inches of water equivalent, respectively. We know what’s happened the past few weeks regarding snowfall, so you can expect higher ranges when the Feb. 25 report comes out.
The deepest snow cover was in far northwest Illinois and southwest Wisconsin, and of course, much of that snow melt goes into the Fox River.
Again, back on Feb. 9, modeled soil moisture values across the area range from slightly below average to slightly above average. Values were highest in southern Wisconsin, at the 70th to 80th
Frost depth ranged from 4 inches to 7 inches across area river basins, with the deepest frost depth values reported in southern Wisconsin.
Despite very cold weather, the good news is that heavy snow pack has reduced the frost depth penetration.
Spring Weather Outlook
The long term (next couple months) outlook from the Climate Prediction Center indicates below average temperatures slightly favored for February, transitioning to above average temperatures slightly favored for spring 2021.
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.