CHICAGO -- Remember to protect temperature-sensitive plants this evening as the Chicago National Weather Service Forecast Office has issued a Frost Advisory (blue shaded area on the highlighted map) from 1AM to 8AM early Wednesday morning calling for temperatures to drop into the lower and middle 30s with a good chance of scattered frost, especially low-lying locations in the northern and western-most locations away from the city along the Fox and Rock River Valleys. Scattered frost may also occur south of Interstate-80, but an increase in high clouds could temper readings in that area.
Clouds will finally begin to thin and winds let up later this afternoon/evening as the intense low pressure system that brought the widespread cloudiness and heavy rainfall to our area finally pulls off to the northeast into the eastern Ontario Canadian Province. We are almost 2 weeks past the date of average last spring freeze (April21), but with cool dry (dew points in the lower 30s) high pressure centering over northern Illinois later tonight, it proves an excellent setup for clear skies, light winds and maximal radiational heat loss.
Another low pressure system already developing in the Texas Panhandle is set to move east-northeast toward the Ohio River Valley Wednesday, and high clouds from that system may spread over the southern portions of our area as early as tomorrow morning, possibly tempering the heat loss in our southernmost sections. If the clouds don’t reach that area, readings could also drop off into at least the middle 30s, creating some scattered light frost in the south as well, especially in lower-lying locations.