DAVENPORT, Iowa — The National Weather Service expanded the range of the excessive heat warning shortly after 3 p.m. to include Jo Daviess, Stephenson, Carroll and Whiteside counties.
Initially, the Quad Cities station had pinpointed Bureau and Putnam counties as requiring the alert shortly after the noon hour.
By 4 p.m., the Quad Cities station issued a tweet showing preliminary heat index readings from across the region. These readings were unverified, it said, but were illustrative of the high temperatures and high humidity. Clinton, Iowa was at 108, Rockford at 100 and Rock Falls-Sterling was at 111.
The warning is in effect until 9 p.m. Towns in the affected zone that also received the heat warnings are Princeton, Hennepin, Freeport, Mount Carroll and Sterling. The Iowa town of Clinton was also included.
Meanwhile, other parts of northwestern and north-central Illinois are under a heat advisory.
All of northern Illinois is part of a hazardous weather outlook for the weekend.
The service says areas under the heat warning may experience heat index values of 105 to 110 degrees.
More broadly, the heat warning extends to parts of northeast Missouri, east and southeast Iowa and parts of Illinois south of Interstate 80.
People in the affected areas are advised that the heat and humidity will increase the potential for heat-related illness. Those participating in outdoor recreational or work activities are especially vulnerable.
People are advised to drink fluids, stay in air-conditioned rooms, seek out public spaces with air conditioning, stay out of the sun and check on relatives and neighbors. Young children and pets should not be left unattended in vehicles under any circumstances.
Those who must be outside should wear lightweight and loose fitting clothing, schedule frequent rest breaks in the shade.
Anyone who is overcome by heat should be moved to a cool location and call 9-1-1 as heat stroke is considered an emergency requiring immediate medical attention.
The following counties are considered part of the heat advisory: Winnebago, Boone, Ogle, Lee, DeKalb and La Salle. The towns of Rockford, Belvidere, Rochelle, Oregon, Byron, Dixon, DeKalb, Sycamore, Ottawa, Streator, La Salle, Mendora and Marseilles are included in the advisory.
For areas under the advisory, peak afternoon heat index values of 103 to 107 degrees are expected. The advisory is in effect until 7 p.m.
The same precautions as for excessive heat are advised.
Hazardous weather outlook
Heat indices could reach into the upper 90s and as high as 105 degrees, according to the outlook issued at 12:33 p.m. Saturday, by the National Weather Service station in Romeoville.
There is also a chance of thunderstorms bringing a risk of lightning strikes come evening. The storms are forecast in areas north of I-88 and I-290.
Counties in the outlook are Winnebago, Boone, McHenry, Lake, Ogle, Lee, DeKalb, Kane, DuPage, La Salle, Kendall, Kankakee, Livingston, Iroquois, Ford, Cook, Will and parts of Indiana.