Metro Detroit Heat Advisory Pushes Heat Index Past 100, Triggers Early School Dismissals and Free Cooling Buses

Temperatures climbing into the low 90s and a heat index topping 100 degrees pushed the National Weather Service to issue a heat advisory across most of Southeast Michigan on Wednesday. The advisory led one Wayne County school district to send students home early and a regional transit agency to roll out free air-conditioned buses at six locations.

The advisory took effect at noon and runs through 8 p.m. for Lenawee, Livingston, Macomb, Monroe, Oakland, Washtenaw and Wayne counties. Detroit's high was expected to reach 94 degrees, well above the city's average September high of 74.4 degrees, according to the National Weather Service. Combined with dew points in the 70s, the heat index was forecast to hit 102 degrees, a level the National Weather Service says can produce heat related illness with prolonged exposure or physical activity.

Plymouth-Canton Educational Park, home to three of Plymouth-Canton Community Schools' four high schools, dismissed students at 10:25 a.m. rather than holding a full day of classes in the heat. "The safety of our students remains our highest priority," the district said in a statement Wednesday morning.

The Suburban Mobility Authority for Regional Transportation sent paratransit vehicles converted into cooling stations to six sites around the region: Macomb Mall in Roseville, Bel-Air Shopping Center on 8 Mile Road in Detroit, the old Phoenix Center in Pontiac, Fairlane Mall in Dearborn, Southland Mall in Taylor, and a stop at Providence Drive and Greenfield in Southfield. The vehicles operated from 11 a.m. to 7 p.m., open to anyone regardless of whether they carry a SMART pass or pay a fare.

"Extreme heat poses serious health risks, particularly for seniors, people with disabilities, young children, and those without access to air conditioning," SMART said in a news release Wednesday morning. SMART called the program part of its work beyond regular bus routes.

Steve Freitag, a meteorologist with the National Weather Service office in White Lake Township, traced the heat to a weather pattern parked over the Ohio Valley. "We had a strong, upper-level ridge over the Tennessee-Kentucky area that's been parked there, and that, with the big surface high, we had a big clockwise circulation bringing in moist air from the Gulf," Freitag said. "Being on the outer fringe of that heat dome, we're getting the warm temps that we've been talking about." He added that the pattern is fairly typical for Michigan this time of year.

Forecasters also flagged a slight risk of thunderstorms Wednesday afternoon and evening as the atmosphere grew more unstable through the day. The National Weather Service said the main concerns were damaging wind gusts and localized flooding, with an isolated tornado also possible, mostly in areas north of Interstate 69. South of the freeway, the odds of severe weather were harder to pin down. "Fortunately, storms have been struggling to develop down our way, but a cold front over the northern Great Lakes is expected to slowly sag south over the next couple of days, so we still have several opportunities to get some thunderstorms and showers over the next three days," Freitag said. "The coverage remains elusive and difficult to predict at this point."

More rain chances follow Thursday and Friday as the front moves through, with a marginal risk for severe storms Thursday along and south of I-96. Humidity is expected to stay high even as temperatures ease, with dew points holding in the 70s.

Relief arrives for the Labor Day weekend. Detroit's forecast high drops to 88 degrees Thursday, 83 on Friday, 80 on Saturday and 78 on Sunday, according to the National Weather Service. Wednesday's heat is far from a record for the date; the hottest Sept. 2 on record in Detroit was 100 degrees, set in 1953.

School districts and transit officials have not said whether Wednesday's measures will extend into Thursday, when forecasters still expect a marginal severe weather risk and lingering humidity before temperatures fall through the weekend.