As intense heat continues to move across the eastern two-thirds of the nation throughout the week, air quality will likely suffer as a result.
The cities plagued most by the heat will be St. Louis, Kansas City, Chicago, D.C. and Philadelphia.
Air quality will deteriorate in these areas, with most of the East and Midwest facing moderate health concern as a result of the air quality.
According to the air quality index at airnow.gov, a moderate health concern means that 'air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.'
Areas of more serious concern include Atlanta, Pittsburgh, St. Louis, Chicago, Detroit, Cleveland and Cincinnati.
These areas have been temporarily deemed unhealthy for particularly sensitive groups. According to airnow.gov, "Members of sensitive group may experience health effects."
The general public is not likely to be affected, the site explains.
It's not a coincidence that poor air quality usually accompanies heat waves.
"When you get a large area of high pressure promoting widespread heat, you also get a large zone of stagnant air," said AccuWeather.com Meteorologist Meghan Evans.
"Smoke and ozone can be trapped in the atmosphere, leading to poor air quality."
For the full story on the heat, click here.
A powerful storm will bring disruptive weather from Spain to France and Italy for Christmas Day.
As California heads into its third consecutive dry winter with no relief in sight, firefighters continue to battle a late-fall blaze in Big Sur.
After several days of unseasonable warmth, bitter cold and rounds of snow will continue to spread across the Western and Central states into this weekend.
Similar to the days prior to Thanksgiving, the worst weather will focus on the days prior to Christmas as millions of travelers take to the roads and skies in the U.S. and southern Canada.
An abrupt and abnormal cold wave gripped parts of southeastern Texas in early December, catching many off-guard, including two native Southern California bobcats recently transferred to the area.
Warm air is forecast to surge into much of the eastern half of the nation by the weekend and will be accompanied by heavy rain and flooding risk in some locations.
Des Moines, IA (1990)
Freezing drizzle with a temperature of -2 degrees F.
N. California & Oregon (1964)
Great warm surge and torrential rains on deep snow cover; record floods followed.
Perey, IL (1967)
An F2 tornado carried women and her baby 400 feet; they survived.