By Karin Matz
CHICAGO (Reuters) - A massive heat wave is expected to develop over much of the central and eastern United States beginning on Friday with heat index values that could reach 115 degrees.
The big story for the coming weekend will be the building heat," said Jim Keeney, a National Weather Service meteorologist. "It looks like it's going to be a long-term heat wave."
In the thick of the heat wave is Oklahoma where Governor Mary Fallin asked Oklahomans to pray for rain this Sunday.
"The power of prayer is a wonderful thing, and I would ask every Oklahoman to look to a greater power this weekend and ask for rain," Fallin said in a news release on Thursday.
Fallin on Thursday also issued a ban on outdoor burning for the western half of the state because of the extreme drought conditions.
"The number of wildfires we have had over the last few months is extremely tough on our state firefighters," Fallin said.
"It's a drain on their resources as well as a physical drain. Anything that can be done to minimize fires will help to keep both our firefighters and the public safe. I'm asking all Oklahomans to be vigilant and to do their part in preventing fires."
Earlier this year Texas Governor Rick Perry asked Texans to pray for rain because of the drought there.
As of July 12, about 72 percent of Texas and 43 percent of Oklahoma are experiencing the worst possible drought conditions, according to the U.S. Drought Monitor.
On Thursday, 10 states were under heat advisories or watches, down from earlier in the week when 24 states were on the list.
"The worst states are Texas, Oklahoma and Louisiana," said Victor Murphy, a weather service meteorologist, who said Texas is seeing the warmest summer on record so far.
Operations at the Denver International Airport were returning to normal Thursday afternoon after hail and rain pelted the area Wednesday night during a severe thunderstorm, leaving 1,000 passengers stranded at the airport overnight.
Among those passengers was Wisconsin Governor Scott Walker, traveling to a National Governors Association meeting in Salt Lake City.
Walker tweeted, "Got stuck in Denver airport & slept on the floor (did get a pillow & blanket)."
Most airlines reported significant hail damage, according to Laura Coale, a spokeswoman for the airport, who said there were reports of damage to 40 planes.
The Denver area will be under a flash flood watch Thursday afternoon and through the evening.
"We are expecting some heavy rains, and there could be some hail with the storms," said Byron Louis, program manager for the weather service in Denver.
(Additional reporting by Keith Coffman and Steve Olafson; Editing by Jerry Norton)