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.
Several storms will bring periods of rain and gusty winds to the west coast of the United States next week with the potential for one of these to reach Southern California.
A dramatic change to colder weather, and in some cases a taste of winter with snow, will take place this weekend.
Rain will continue to cause travel delays and raise the risk of isolated flooding in parts of the northeastern United States and Atlantic Canada into the weekend.
The changing of the seasons will bring beneficial rainfall to northern Brazil, a region that has experienced severe drought over the past several years.
Damaging storms pounded the Pacific Northwest, while two powerful typhoons struck the Philippines within a four-day span.
Typhoon Haima made a second landfall in southeastern China on Friday after leaving at least 13 dead in the northern Philippines.
Ottawa, Canada (1988)
Record October snowstorm brings 21 cm (just over 8 inches).
Hurricane Juan kills more than 200 and results in $1.5 billion in damages.
Tuscaloosa, AL (1994)
Lightning struck during Alabama-Mississippi football game. 3 people were injured.