Temperatures did bottom-out in the low to mid 30s along and north of Interstate-80 early this Tuesday morning with scattered frost reported at many locations, verifying the Frost Advisory that was in effect. There was extensive cloudiness earlier in the overnight hours, but clearing occurred after 4AM, allowing readings to drop and frost to form.
Lowest temperatures were 30-degrees at Rochelle, Waukegan and Freeport. Just across the state line in southern Wisconsin the skies were clear for a longer period and the air a little drier (dew-points in the middle 20s), allowing temps to drop into the upper 20s – observed 28-degrees at Burlington and 29-degrees in Kenosha. South of Interstate-80 clouds persisted into the forenoon, and as a result temps held in the upper 30s and lower 40s.
Tonight the center of a slowly modifying cool Canadian-source high pressure air mass will drift slowly southeast out of Minnesota into south-central Wisconsin, allowing that lower dew-point air to nose farther into northeastern Illinois/northwest Indiana. While there may be some higher cirrus clouds, the lower stratocumulus clouds we experienced last night and early this morning should slide off to the south and east, allowing better long-wave radiation and ultimately colder early morning lows Wednesday morning. There is a good chance for an area-wide Frost Advisory tonight/Wednesday morning.
Following is a list of low temps this morning at area airport locations…
Du Page/West Chicago…33