What Does A Slight Risk For Severe Mean?
The Storm Prediction Center (or SPC) has placed northern Illinois in the slight risk category for severe weather today (3/19/20). The SPC has five levels of risk for severe weather that include (from lowest to highest) marginal, slight, enhanced, moderate and high. Slight is the second lowest of the five levels but it doesn't mean we can let our guard down. Nashville was in a slight risk category in early March and the outbreak that hit Tennessee at that time produced ten tornadoes in the state and one of them was an EF-4 with winds of 175 mph. It is rare to get that type of a tornado outbreak in an area with a slight risk though. According to the SPC a slight risk means "short-lived and/or not widespread isolated intense storms possible."
The office breaks it down further to include the following possibilities in a slight risk area:
One or two tornadoes
Reports of strong winds/wind damage
Hail around 1", isolated 2"
Of all the significant tornadoes to strike the Chicago area that include F2 tornadoes (winds 113 to 157 mph) or stronger, almost 10% have occurred during March.
One of the most deadly struck on March 28, 1920. It was an EF-4 tornado with a track over 53 miles long from Channahon to Wilmette and finally out over Lake Michigan. 20 people were killed and 300 injured.
So whether it is a marginal risk or a high risk, we have to be especially vigilant when it comes to severe weather. Be sure to have a weather radio and at least one other source for severe weather alerts.