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.
Between 3 and 6 feet of snow and plunging temperatures have left thousands snowed in over upstate New York, and the cold and snow has taken lives.
A storm riding a surge of springlike warmth will bring a round of severe weather including the risk of a few tornadoes this weekend in the South as Thanksgiving travel begins.
After a pause in the lake-effect snow on Wednesday, more bands of heavy snow will continue to pummel areas downwind of the Great Lakes, including northern and western New York, Thursday into Friday.
A shift in the weather pattern in early December will deliver some relief for the 200 million people across the U.S. being blasted by bitter air.
There will travel trouble spots for Thanksgiving travel through Wednesday including areas of winterlike conditions and rain-related issues.
Following waves of arctic cold and snow, more typical of January, a few days of springlike weather are on the way for the South, Midwest and Northeast starting this weekend.
Rapid City, SD (1996)
Temperature at Rapid City was 21 degrees. At an elevation of 5,000 feet, it was 50.
Williams Village, NY (2000)
22" of lake effect snow.
British Columbia (2002)
After a long dry spell where reservoirs were very low, a two week rainy spells resulted in flooded basements. 6.30 inches of rain fell in the lower mainland.