Flower Mound and Highland Village face heat index values up to 108°F on Tuesday, Aug. 18, under an Extreme Heat Warning the National Weather Service issued Monday afternoon.

The NWS Fort Worth office posted the warning at 12:45 p.m. Aug. 17, covering Denton County and 27 other North Texas counties. The warning takes effect at noon Tuesday and runs through 8 p.m.

It replaces a Heat Advisory already in effect through noon Tuesday. The advisory carries heat index values up to 106°F; the warning escalates to 108°F.

Conditions are already dangerous. At Denton Enterprise Airport, the temperature reached 105°F with a 108°F heat index at 4:53 p.m. Monday, according to the NWS Denton County forecast.

The NWS urged residents to stay indoors between 2 and 7 p.m., when heat peaks, drink plenty of water and rest in shade if outdoor activity is unavoidable.

Where to find cooling centers

Denton County's cooling centers page lists locations the county says are open daily from 10 a.m. to 7 p.m. Residents can also call (940) 566-1308 or dial 2-1-1 to find the nearest center. The statewide 2-1-1 Texas line, reachable at (877) 541-7905, connects callers with cooling resources across the region.

Who is most at risk

The NWS warning flags people without reliable shelter as especially vulnerable and urges residents to check on relatives and neighbors. Children and pets must never be left in enclosed vehicles, even briefly.

Heat stroke is a medical emergency. Anyone showing signs should call 911 immediately.

Heat won't break soon

The NWS forecast projects heat index values up to 111°F on Wednesday, Aug. 19, and up to 110°F on Thursday, Aug. 20, suggesting additional warnings may follow.

Neither the Town of Flower Mound nor the City of Highland Village had posted public statements addressing the Extreme Heat Warning as of Monday evening. The Fort Worth Star-Telegram reported the warning covers a wide swath of North Texas.

The NWS Fort Worth office will post updates and any extensions beyond Tuesday's 8 p.m. expiration.