Temperatures Wednesday warmed into the upper 70s and low 80s, officially reaching 82 degrees in Rockford. This was the fifth straight day where the high temperature reached 80 degrees, or higher. But some big changes are on the horizon, beginning Wednesday night.
Shifting winds around to the northeast late Wednesday will usher in a cooler air mass as high pressure builds to the north. In fact, an unseasonably cold air mass for late May settles in across much of the Great Lakes Thursday and Friday. Overnight lows Wednesday will dip into the low 50s, only warming into the low 60s Thursday. Temperatures, however, on Thursday are going to be heavily dependent on the placement of a warm front. This warm front will be stretching from central/northern Illinois, westward to an area of low pressure that’ll be sweeping through the Plains. That low is currently bringing severe weather to parts of Nebraska, Kansas, Oklahoma and Texas Wednesday evening.
Skies will remain dry and mostly clear for much of our Wednesday evening but cloud cover will increase overnight. Ongoing thunderstorms west of the Mississippi River Thursday morning should be in a weakening phase as they near northern Illinois and southern Wisconsin. Dry air initially will limit our rainfall chances during the morning, but we’ll see that chance increase by late morning and early afternoon.
Temperatures cooling off into the upper 40s and low 50s Wednesday night will only reach the low 60s Thursday afternoon as a warm front stalls just to the south of the immediate area. South of the boundary temperatures are likely to climb into the 70s and 80s. It’s possible, though, that the boundary could lift as far north as Whiteside, Lee and DeKalb counties placing a portion of the viewing area in the ‘warm sector’. While the overall severe risk for our region is low, if the warm front does lift a little further north there could be an increased risk for a few stronger storms late in the day Thursday. Rain showers will be steady through much of the afternoon Thursday as moisture lifts up and over the relatively stable air near the surface. As the low pressure system approaches from the west it’s possible that a few thunderstorms could occur during the evening. With an increase in moisture a swath of heavy rain may also fall for a portion of the area where rainfall totals could come close to an inch or more.
The low will be quick to pull away Friday morning but an increase in the east wind and thick deck of low clouds will hold temperatures in the 40s and 50s Friday afternoon! Winds will also be gusty from the east at around 30 mph. Lightly scattered rain showers will be possible through the afternoon.