By Karin Matz
CHICAGO (Reuters) - The stubborn heat wave blasting the U.S. midsection was blamed on Tuesday for another death and triggered alarms along the U.S.-Mexico border, where immigrants crossing illegally faced harsh conditions.
The core body temperature of a 65-year-old man who died while mowing his lawn near Wichita, Kansas, was 107 degrees, said Butler County Sheriff Kelly Herzet.
"It's tragic," Herzet said. "People need to stay in when it's this hot, or drink plenty of liquids. They need to know their limits."
Heat, the leading weather-related killer in the United States, has resulted in at least 13 deaths across the Midwest since last week, the National Weather Service said.
The high temperatures were also responsible for an alarming spike in deaths of illegal immigrants trying to cross into the United States, according to the U.S. Border Patrol.
"Cases of dehydration and heat exhaustion are way up," said supervisory agent Dan Milian, with the Rio Grande Valley sector in Edinburg, Texas.
"We are seeing it with elderly people, young children and all people who try to make it through the brush country in this heat."
As a result, the patrol deployed search and rescue units in the south Texas brush country.
In Omaha, Nebraska, flood control work along the overflowing Missouri River was halted due to the heat, as officials worried that filling sandbags was too strenuous.
There were jaw-dropping heat indexes -- measured as a combination of temperature and humidity -- across the Midwest. It felt like 131 degrees in Knoxville, in central Iowa, and 124 in Freeport, Illinois, the Weather Service said.
"This is completely out of whack for the Upper Midwest," said Chris Vaccaro, a Weather Service spokesman. "We've got several more days on tap" of excessive heat.
Parts of 23 states were under some sort of heat advisory or warning. The blanket of heat was expected to expand eastward in coming days, with actual temperatures expected to flirt with 100 degrees in Washington, D.C., and in New York.
Along with the heat, patchy but severe thunderstorms were forecast across the upper Midwest, through the Ohio Valley and into the mid-Atlantic region. Where the storms hit, humidity could become even more stifling afterward, Vaccaro said.
Thunderstorms in Cleveland late on Monday left more than 20,000 residents without power.
In Illinois, the second-largest corn and soybean producing state, the heat and humidity were not yet damaging crops, according to University of Illinois agronomist Emerson Nafziger. But a lack of rain was cause for concern.
"Corn is holding on so far," Nafzinger said. "We're starting to get a little worried right now from a water standpoint."
(Additional reporting by Jim Forsyth, Kim Palmer, David Hendee, Kevin Murphy and Karen Brooks; Writing by Karin Matz; Editing by Andrew Stern and Jerry Norton)