MINNEAPOLIS, July 18 (UPI) -- A potentially dangerous mix of heat and humidity gripped the U.S. midsection Monday, with temperatures heading for the 100s in some states.
Forecasters said the hottest weather will be in the Plains and Mississippi Valley region through the first half of the week. Later in the week, temperatures in the major East Coast cities along Interstate-95 could approach triple digits.
The hottest spots in Oklahoma through South Dakota expected highs topping 100 and temperature in the 90s were forecast for most of the rest of the country, except for some mountain and coastal regions, CNN reported.
The National Weather Service warned parts of Minnesota and Wisconsin of heat-related illnesses, issuing an excessive heat warning through Wednesday, the St. Paul Pioneer Press reported. Temperatures in the 90s were forecast all week.
In some areas, heat index values -- or how hot it feels outside -- topped 125 degrees, the NWS said. The value describes how intense heat feels and includes factors such as humidity.
Jacob Beitlich, a Des Moines, Iowa, meteorologist for the NWS, told CNN two factors make this heat wave dangerous: the lack of a significant drop in overnight temperatures to allow people's bodies to cool and relatively high humidity, which makes it feel noticeably hotter than the thermometer indicates.
"That takes a toll on your body," Beitlich said. "When it's more humid, it's more difficult to cool down from sweating."
The Missouri Department of Health and Senior Services said there have been 618 emergency room visits for heat-related illnesses so far this summer, USA Today reported. Officials in Missouri confirmed two heat-related deaths in St. Louis and nine suspected deaths in the Kansas City area.
Across Missouri, scores of cooling centers were set up in libraries, senior centers, schools and other sites.
At Target Field in Minneapolis, Minnesota Twins fans stood in long lines to get water from coolers, used spray fans and wrapped wet towels on their heads during a Sunday afternoon game under the blazing sun.
This week's severe heat wave could leave its imprint on record books, jeopardizing numerous high-temperature records as the sizzling heat spreads east, AccuWeather.com said.
