Dangerous heat set to arrive across southern Wisconsin; strong to severe storms possible Wednesday night

A dangerous combination of heat and humidity is set to overtake southern Wisconsin on Thursday and intensify on Friday, the National Weather Service said Wednesday.

But before the heat arrives, the area could see severe storms on Wednesday night. 

First, the heat: The weather service has issued a heat advisory for all of southeastern and south-central Wisconsin, including the Milwaukee and Madison metro areas. 

The heat index — what the temperature feels like when combined with humidity — could reach as high as 110 in the region by Friday afternoon. 

"Highs will reach the lower 90s Thursday afternoon, with heat index values of 100 to 106. Highs will reach the middle to upper 90s on Friday, with heat index values of 103 to 110," the weather service office in Sullivan said in a statement.

"Heat illnesses will be possible with prolonged outdoor exposure to the heat," the statement said. "Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun and check up on relatives and neighbors."

The heat is set to affect much of the United States. More than 115 million Americans live where some level of heat alert is in effect.

The National Weather Service has issued excessive heat warnings and watches as well as heat advisories in the Plains, Midwest, Ohio Valley and parts of the East. 

Electricity demand set to spike

Folks who monitor the nation's electricity grid are preparing for power demand to soar.

The Midwest Independent System Operator (MISO), an organization that oversees the flow of electricity across Wisconsin as well as 14 other states and the Canadian province of Manitoba, has declared what's known as a capacity advisory for Friday.

That essentially helps members of the organization plan for major demand for electricity across the region's power grid. 

"We are working proactively to ensure power system reliability ahead of forecasted high temperatures," Allison Bermudez, a spokeswoman for the organization, said via email.

MISO, as well as Milwaukee utility We Energies, said they anticipate being able to meet electricity demand.

Preparing for busy stretch

Bell Ambulance in Milwaukee has already put its heat plan in place, said Jim Lombardo, executive vice president and partner at the Milwaukee-based medical transport company. 

All its ambulances are stocked with coolers full of ice and nearly every employee at the company is prepared to respond to calls for help.

The hot weather tends to aggravate underlying health conditions, Lombardo said. 

"That two-block walk to the store that normally is no problem suddenly becomes a problem," in this kind of heat for folks who have pre-existing health conditions, Lombardo said.  

Cool spots

Milwaukee Mayor Tom Barrett reminded people to be aware of the heat's impact.

"We're very, very concerned about people with physical challenges," Barrett said at a news conference Wednesday. "We're concerned about the elderly. We're concerned about children."

He asked residents to "please be a good neighbor" and check on seniors and people with underlying health conditions. 

That includes making sure children are not left unattended in cars, the mayor said.

The city will be operating cool spots in which fire hydrants are hooked to massive sprinklers that will spray water on residents at four playgrounds in the city. 

The cool spots are:

• Ben Franklin School, 2308 W. Nash St.
• Carmen Playfield, 7320 W. Carmen Ave.
• Franklin Square, 2643 N. 13th St.
• 3818 N. 8th St.

Barrett also invited residents to visit one of the city's libraries, which have been designated as cooling sites.

Put your garbage and recycling out early

On Thursday and Friday, Milwaukee Department of Public Works garbage and recycling pickup will begin an hour earlier than normal "to minimize the amount of time sanitation crews have to work in these (hot) conditions", the city said in a statement.

Residents should have their carts out and accessible for collection the night before their scheduled pickup or by 6 a.m. on the scheduled day.

Cooling centers open in Waukesha County

Waukesha County Executive Paul Farrow said in a statement Wednesday that cooling centers in the county will be open as the heat arrives. Residents should call 211 to locate a cooling center. (The statement said 211 does not have resources to help residents obtain fans.)

"Dozens of cooling centers and places to cool off are located in Waukesha County," according to the statement. "The public may use Waukesha County ice arenas as free cooling stations during business hours."

The cooling centers include:

• Naga-Waukee Park Ice Arena, 2699 Golf Road, Delafield, weekdays from 12:30-2:30 p.m. and weekends from 3-5 p.m..
• Eble Park Ice Arena, 19400 W. Blue Mound Road, Brookfield, noon to 2 p.m. Sunday through Friday
• Retzer Nature Center’s Environmental Learning Center, S14 W28167 Madison St., Waukesha, 8 a.m. to 4:30 p.m.

Hottest so far this year

It hasn't been this hot in southern Wisconsin since the end of June and beginning of July last year, according to the weather service. 

The highs of 94 forecast for Thursday and 96 for Friday in Milwaukee are well above the normal high temperature of about 80 this time of year, according to the weather service. 

"Friday is going to be nasty, there's no doubt," said Ben Miller, a weather service meteorologist in Sullivan.  

The good news is the heat won't last long. A cold front is expected to make its way into southern Wisconsin and bring some relief to the region on Saturday, Miller said. 

Salvation Army opens cooling centers

The Salvation Army said Wednesday that because of the heat, it is opening cooling centers in Milwaukee and Greenfield.  

"Everyone deserves comfort and a safe place to go during the extreme heat," Major Steve Merritt, divisional commander for the Salvation Army of Wisconsin and Upper Michigan, said in a statement.

The cooling centers and their hours are:

• Citadel Corps Church and Community Center; 4129 W. Villard Ave., Milwaukee; 9 a.m. to 4 p.m. Monday-Friday.
• Coldspring Church and Community Center; 2900 W. Coldspring Road, Greenfield, 9 a.m. to 3 p.m. Monday-Thursday and 9 a.m. to 1 p.m.  Friday.

Severe storms possible Wednesday night

Meanwhile, all the heat and humidity across much of Wisconsin and the Midwest is likely to kick off a round of thunderstorms Wednesday night into Thursday morning. Some of the storms could turn severe, especially west of Milwaukee, the weather service said. 

"A complex of thunderstorms is likely to move into south central Wisconsin later this evening and overnight, spreading across the rest of the area overnight into early Thursday morning," according to a statement from the weather service office in Sullivan. "There is a slight risk for severe storms over south central Wisconsin tonight, with a marginal risk to the east."

Damaging winds are the main hazards, along with heavy rainfall. A flash flood watch has been posted for areas of southwest and west-central Wisconsin.

"There is some question about how long the line (of storms) holds together before it weakens," as it moves east said Miller. 

USA TODAY contributed to this report. Contact Joe Taschler at (414) 224-2554 or jtaschler@gannett.com. Follow him on Twitter at @JoeTaschler or Facebook at facebook.com/joe.taschler.1.