A weak ridge is bringing very pleasant weather across northern Illinois and southern Wisconsin today, temperatures under mostly sunny skies will warm to 73°. A few localized spots could make it to 75° making temperatures about 8-10° above average for this time of year. High clouds will slowly increase this afternoon and skies overnight turn cloudy. We'll get another day in the 70's Tuesday, before our temperatures begin to fall.
You'll notice highs in the 60's on Wednesday with a passing cold front and widespread showers. Behind that front we'll notice down right chilly temperatures, highs on Thursday won't even make it out of the 50's. Overnight lows Thursday and Friday morning will fall into the mid and upper 30's, and this would bring a threat for frost.
One component we will watch for however will be the cloud cover, if clouds move in and thicken up temperatures then would be a few degrees warmer. If skies stay clear or mostly clear, this would allow for temperatures to fall closer to dew points, which as of now are forecast in the mid and upper 30's. Cloud cover typically acts as an insulator, keeping heat trapped at the surface. But, when there is a lack of cloud cover, the heat is able to escape back into the atmosphere and temperatures fall.
So, at this time it is a bit too soon to say for sure if we will see frost or not Thursday and Friday mornings, but we will keep you updated as we get closer!