Updated at 1:28 p.m., EST:
Two runners who collapsed early Sunday during the Philadelphia Marathon have died.
WPVI-TV reported that two males, a 21-year-old and a 30-year-old, first collapsed along the 2200 block of the Ben Franklin parkway. At the time, officials said the runners had no vitals.
They were rushed to Hahnemann Hospital, where the young men were pronounced dead.
Professor of Exercise and Sport Science at Penn State University, Scott Kretchmar, said in October that warmer weather increases the chances that a runner will become overheated and dehydrated.
He said the ideal temperatures for runners is in the mid- to upper 40s.
Temperatures in Philadelphia have been rising through the 50s Sunday morning with comfortable humidity (dew points in the mid-40s). The city will see a high of 64 degrees this afternoon, which is warmer than usual.
"That is mild for this time of year, but not record-breaking," AccuWeather.com Senior Meteorologist Kristina Pydynowski said.
She said the average high for Nov. 20 is 54 degrees, and the record high is 76 degrees from 1985.
"Today's high is more typical of late October," she said.
Results from a U.S. Army Study, reported by Running Planet, support Kretchmar's remarks. The study found that faster performances correlated with cooler temperatures, specifically, at 51-55 degrees for men and 53-57 degrees for women.
The study also found that temperatures as low as 41 degrees have the potential to give runners an even bigger boost.
Kretchmar said it's important to follow the "20-degree" rule by dressing as if it is 20 degrees warmer than it actually is. He emphasized the importance of wearing clothes with ventilation.
Cause of death for the men is unconfirmed at this time.
San Francisco will see abundant sunshine through at least Thursday.
Temperatures will remain in the 90s across the Metroplex through at least Thursday.
lightly above-normal temperatures are expected through the Labor Day weekend across the Los Angeles area.
Minneapolis is on the front line of a severe weather outbreak this Labor Day weekend.
After an earthquake hit in the area, the Bardarbunga volcano erupted Friday in Iceland, causing a temporary no-fly order.
The North Central states face the most adverse weather this Labor Day weekend, in the form of severe storms and tornadoes which will threaten lives and travelers.
East Coast (1954)
Hurricane Carol hit with the single greatest property loss to date.
Raleigh, NC (1965)
46 degrees -- coldest ever in August.
Three inches of snow fell in parts of the state; record lows were set in 31 northeastern U.S. cities and towns.