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.
See how far away severe thunderstorms are as we monitor the severe weather with these radar images.
Heavy rain returning to the northern Plains will generate a renewed flood threat for the Red River.
Mount Saint Helens has erupted several times since the destructive 1980 eruption, and likely will again in the future.
Seven homes have been red tagged, meaning do not occupy, and six others are under a voluntary evacuation order.
Though recovery continues from Superstorm Sandy, residents and homeowners on the Atlantic coast should prepare for another active season in 2013.
While there is a threat for a shower in spots in Baltimore, Md., today, it will not be a washout like the day of the Kentucky Derby.
Moorcroft, WY (1978)
27 inches of snow (17th-20th), bringing total for the month to 92 inches.
Houston, TX (2000)
6.80" of rain.
Sibi, in the northwest, had a high of 115 with a dewpoint of 90. The RealFeel was 150 degrees.