A FREEZE WARNING has been issued for northern Illinois beginning at Midnight Monday night, lasting through 7am Tuesday as temperatures are forecast to fall close to, or slightly below, freezing Tuesday morning.
Cloud cover has been rather thick throughout much of Monday afternoon limiting just how warm temperatures were able to rise. Officially the high temperature made it to 50 degrees in Rockford, but that was achieved earlier in the day. As clouds thickened and wind speeds increased, temperatures dropped back into the 40s and currently sit in the low to mid 40s, with a few upper 30s across NW Illinois. Winds have been rather blustery, gusting to around 30 mph at times throughout the day. While the wind gusts will calm through the evening, sustained winds will remain between 5-15 mph, pushing wind chills Tuesday morning down into the 20s.
How far temperatures fall Monday night will depend on just how quickly the cloud cover clears from the Stateline. While there have been some pockets and holes in the generally cloudy afternoon sky, cloud cover is still fairly thick and expansive back over eastern Iowa and Minnesota. And with a little more of a reinforcement of cold air Monday evening, the clouds may stick around through much of the night. If that occurs, temperatures won’t get quite as cold and could remain a few degrees above freezing. If, however, clouds clear and there is a few hour window of mostly clear skies then widespread temperatures at, or slightly below, freezing can be expected Tuesday morning.
Frost Monday night shouldn’t be too much of an issue as winds remain elevated through Tuesday morning. Frost may become a higher concern, though, Tuesday night into Wednesday with high pressure overhead, mostly clear skies and a much lighter wind. Cloud cover is expected to increase, though, by Wednesday morning.
For tonight, you’ll want to make sure you cover any vegetation that may be sensitive to the cold to eliminate the risk of it freezing. And you’ll likely need to cover your plants again Tuesday night with the risk for frost Wednesday morning. This late Spring freeze is actually pretty close to when, on average, northern Illinois typically experiences it last Spring freeze; usually within the last week, or so, of April. The earliest Spring freeze occurred back in 2017 on April 7th and the latest was in 1992 on May 27th!