Update: 6:28 p.m.: The National Weather Service issued an alert that a second line of strong to severe thunderstorms is approaching northeastern Illinois.
Damaging winds and large hail — half-dollar in size — will accompany these storms.
However, a tornado threat is shifting north along the Wisconsin-Illinois border.
The area remains under a tornado watch until 8 p.m. — as it has for most of the afternoon.
Earlier: Conditions are favorable for a tornado Saturday, the National Weather Service said.
Most of northern Illinois, including McHenry, Kane, DeKalb, Will, La Salle, Grundy, Kendall, Putnam, Bureau, Whiteside, Lee, Ogle, Marshall, Livingston and Carroll counties are under a tornado watch until 8 p.m. Saturday.
Conditions are favorable for thunderstorms to develop later this afternoon. Storms could produced hail, gusts of up to 70 mph and possibly a tornado, according to the National Weather Service.
Officials advise residents move indoors when they hear thunder or see lightning and have multiple ways to check for weather warnings.
In the event of a tornado warning, go to the basement or an inside room without windows on the lowest floor (bathroom, closet, center hallway). If possible, avoid sheltering in any room with windows. For added protection get under something sturdy (a heavy table or workbench). Cover your body with a blanket, sleeping bag or mattress.
Storms are expected to taper off after 8 p.m. Sunday should bring some sunshine with a mostly cloudy sky and high temperatures in the 50s, according to AccuWeather.