By 6:35 a.m. EDT Friday, July 17, the McGhee-Tyson observation was already hinting at a swampy kind of day: partly cloudy skies, about 77°F, and oppressive humidity that made it feel sticky before breakfast. Patchy fog is likely through the early morning, with scattered showers and thunderstorms expected by afternoon. Highs should land near 90-91°F, and the heat index is set to spike near 100-102°F.
Afternoon Storms And Flooding Risk
Showers and thunderstorms are expected to fire up late this afternoon into the evening, with most neighborhoods facing roughly a 40-60% chance of rain and brief, heavy downpours. The National Weather Service warns that "flash flooding could quickly develop" where storms repeatedly track over the same spots or over ground already soaked earlier this week, so be ready for sudden, intense rainfall.
When To Expect Rain
Patchy fog should fade by mid-morning, with only a slight chance of showers before about 11 a.m. Storms become more common from the late afternoon into early evening, roughly between 2 and 7 p.m. The chance for showers lingers overnight. Most areas will likely pick up a few tenths of an inch of rain, but any given thunderstorm could dump heavier pockets in a short time.
Weekend Outlook And Heat
The on-and-off storm pattern hangs around through Saturday and Sunday. Both days bring a solid chance of showers and thunderstorms, with daytime highs in the upper 80s. Humidity will keep heat indices hovering in the upper 90s, so it will feel every bit like midsummer. Local reporting last week noted Knox County opening cooling centers and urging residents to double-check operating hours — see cooling center details and resources for more information.
What You Should Do
Plan on rain gear and some patience for outdoor events, ballgames, and evening commutes. Do not drive through standing water, even if it looks shallow, and allow extra travel time when storms are active. If you or someone you know is vulnerable to heat, spend the hottest part of the day in air-conditioned spaces, drink plenty of water, and call 211 for help locating a nearby cooling center.
