(CNN) -- Large portions of the United States were expected to continue to experience temperatures at or near the triple digits Tuesday, with no relief in sight until at least the weekend.
"Much of the southern Plains into the Lower Ohio Valley down to the Lower Mississippi Valley is covered by heat advisories and excessive heat warnings, where it's going to feel like 100 to almost 110 degrees this afternoon," said Mike Eckert, senior branch forecaster at the National Weather Service in Camp Springs, Maryland.
Advisories will be in place in at least a dozen states, he said, and that could expand eastward later this week into the Mid-Atlantic states around Washington, D.C., and Philadelphia.
As high as the mercury is rising, the main problem is not the heat, but the humidity.
"The temperatures are not really record-breaking, but we've got such high humidity levels that it feels so oppressive outside," Eckert told CNN Radio.
The hottest places in the country Monday were over the southern Plains, particularly in Kansas. Wichita, Kansas, reached a high of 103 degrees and the city of Hutchinson in the central part of the state reached 105.
Throughout the region, residents took steps to try to beat the heat. Marlene Anderson, 60, of Oklahoma City, cooled off at a local senior center.
"My kitchen is very hot and I cannot cook in it, so yes, this is a lifesaver for me," Anderson told CNN affiliate KWTV.
DeSoto, Texas, was expected to see temperatures in the triple digits through the next few days -- hardly ideal conditions for football practice at DeSoto High School. The team's head athletic trainer, Scott Galloway, said efforts are being made to help the student athletes cope.
"Our guys have unlimited access to water, and we provide student trainers and water to every station," Galloway told CNN affiliate WFAA.
Players are also being given ample break time, he said.
"There's a limit to the amount of quality reps you can get out of an athlete when conditions are so unfavorable on the body," Galloway said.
The National Weather Service's Eckert didn't predict much in the way of short-term relief for states feeling the brunt of the heat wave.
"The heat will slowly spread eastward, and then it does look like maybe over the weekend we will see a little bit of relief along the northern edge of the heat," he said.
The heat isn't the only extreme weather expected to cause problems Tuesday. Heavy rain will continue in portions of Colorado, Nebraska, Iowa and Illinois.
Eckert said parts of Iowa and Illinois were receiving two inches of rain per hour early Tuesday. Some of those areas received as much as five inches of rain Monday, and the National Weather Service has issued flash flood warnings in the region.