As the US continues to be plagued by wildfire smoke and sweltering temperatures, more than 170 million Americans are either under heat or air quality alerts.
Health officials have labeled the air quality "unhealthy" across a sizable portion of the Midwest and Mid-Atlantic.
While this is going on, western cities like Las Vegas and Phoenix are preparing for temperatures as high as 43C (110F) this weekend.
In the last few days, at least twelve people have passed away from heat-related causes.
Although conditions have slightly improved in some areas of the Midwest, the poor air quality has been blamed on the more than 500 active wildfires in Canada that have sent smoke plumes south.
A large area of land extending from Michigan and Ohio to the East Coast was predicted to experience the worst air quality in the nation on Friday.
New York City had the worst air quality in the US at around 9:00 local time (14:00 BST) on Friday, followed by Washington, DC, Detroit, and Chicago, according to IQAir.com. .
The elderly, young children, and outdoor workers are considered to be "sensitive groups," according to the Environmental Protection Agency, and the air in these areas is either "unhealthy" or "unhealthy".
The state-wide air quality advisory issued by the authorities will be in effect through Friday. "Take precautions to protect your health," Governor Kathy Hochul urged New Yorkers.
Numerous outdoor activities were postponed in the Washington, D.C., area due to air quality issues, and local health officials issued a warning to stay away from physically demanding outdoor activities and to think about wearing a mask when outdoors.
While this is happening, millions of people in California, Nevada, and Arizona can expect excessive heat warnings to start on Saturday, with some locations expected to reach 43C.
Temperatures have started to fall in Texas, where they have been above 37C for almost two weeks. The state's Webb County, which is centered on the city of Laredo near the Mexican border, has reportedly seen 11 deaths from heat-related causes.
"Our protracted stretch of advisories/warnings for heat will come to an end," the National Weather Service said in a bulletin. "Although a few locations across Central and East Texas may reach advisory criteria, the prevalence of 105F [43C] heat indices will be far less widespread.".
Temperatures are predicted to fall over Saturday and Sunday as a result of storms that are anticipated in other regions of the south.
According to CDC statistics, there are over 700 heat-related fatalities each year, and another 68,000 people are treated in emergency rooms.
According to scientists, human-induced climate change has led to an increase in the frequency, intensity, and length of heatwaves.
There have been some warnings that more wildfires and subsequent smoke alerts are likely as a result of climate change.
A study from the University of California - Irvine that was released on June 12 found, for instance, that "an increase in temperatures and dryness has been identified to be one of the major drivers" of summer forest fires.