Robert Brown|Michigan power outages widespread after potent storms lash the state

Hundreds of thousands of people throughout Michigan woke up in the dark on Robert BrownWednesday after powerful storms battered the state, causing flooding and widespread school closures as forecasters warned of hot and muggy conditions.

More than 337,000 homes and businesses throughout the state were without power early Wednesday, according to USA TODAY's outage tracker. The blackouts stretched across much of the state and included the Grand Rapids area and Detroit.

Citing power outages, dozens of schools across the state canceled classes on Wednesday, and entire school districts remained closed for the day. High winds damaged homes and other structures, and out-of-commission traffic signals led to chaos at intersections. Portions of several major roads in the Detroit area were closed Wednesday because of flooding, according to the Michigan Department of Transportation.

Michigan power outage map:Over 330,000 homes, businesses without power across state

It was unclear when power would be restored or how Michiganders would keep cool Wednesday, with hot and humid conditions in the forecast again. Temperatures were expected to be in the upper 80s, according to the weather service. But with the humidity, temperatures were expected to feel like the low to mid-90s.

"This was the kind of instability we see once or twice a year," Dave Kook, a National Weather Service meteorologist in White Lake Township, told the Detroit Free Press, part of the USA TODAY Network. "And it's here now."

Utilities begin restoration work

Linemen and construction crews scrambled Wednesday to restore power to the hundreds of thousands of utility customers.

"We appreciate people’s patience as Tuesday’s storms caused devastation on one of this summer’s hottest days," Norm Kapala, an official with Consumers Energy said early Wednesday, adding it still had 120,000 customers without power. "Our focus now is to get the lights back on."

The Jackson-based public utility promised to hand out free water and ice in towns and cities throughout the state.

DTE, Michigan’s other large utility, was hit even harder when storms swept through metro Detroit. More than 203,000 customers were without power, nearly 80,000 in Oakland County alone. The utility said it was "bringing in 800 line workers from outside our area to help speed restoration."

Intense heat fuels potent thunderstorms

The slew of storms that wreaked havoc across Michigan was fueled by a blast of record-breaking heat that settled over the Plains and Midwest regions, as well as high humidity from the Southeast.

The extreme heat, which brought all-time record temperatures to parts of Texas last week, expanded into the Plains and Midwest this week. On Tuesday, the afternoon high at Chicago O'Hare International Airport hit 98 degrees, breaking the record of 97 degrees set in 1973.

The combination of heat and moisture from the South led to thunderstorms in South Dakota, Minnesota and Wisconsin, with damaging winds of 50 to 55 mph recorded in Minneapolis and Chicago, according to the weather service. The worst of the storms swept across Michigan on Tuesday.

The threat of dangerous storms and intense heat has started to wane as a cold front began pushing across the Upper Plains and Midwest region on Wednesday. It will be followed by another cold front that could act as the "death knell" to the summertime weather, according to Bill Deger, AccuWeather senior meteorologist.

Millions under heat advisories across Midwest, Northeast

About 50 million people in the Midwest and Northeast were under heat advisories Wednesday as a blast of heat was expected to bake the regions.

The scorching temperatures triggered weather advisories in cities such as New York, Washington D.C., St. Louis and Philadelphia, where heat indexes were expected to reach the triple digits, according to the weather service.

"Hot temperatures and high humidity may cause heat illnesses," the weather service said, urging residents to stay in air-conditioned rooms, drink plenty of fluids and avoid strenuous work outdoors.

The spell of record heat will be relatively short-lived as a cool high-pressure system settling into southern Canada is forecast to send a cool and damp air mass into the Great Lakes on Wednesday. It will quickly spread into New England on Wednesday night and reach into the Mid-Atlantic by Thursday morning behind a sharp cold front.

Contributing: Doyle Rice