Hazy and dangerous fumes from ongoing wildfires in Canada have engulfed the skies over much of the East Coast, prompting serious air quality alerts in over a dozen states.
MORE: Wildfire smoke map: Which US cities, states are being impacted by Canadian wildfires
Canadian officials said firefighters are scrambling to put out the blazes. So far this wildfire season, Canada has seen more than 8.7 million acres burned -- an area larger than the state of Vermont.
The large plume of hazardous wildfire smoke that moved through New York City on Wednesday drifted into the Mid-Atlantic Thursday, bringing dangerous air conditions to Philadelphia, Baltimore, and Washington, D.C.
By Thursday night, the thickest smoke will continue to spread over the Mid-Atlantic. AQI values may reach 400 in some areas. (Levels under 100 are generally considered safe.)
By Friday morning, the hazardous haze will be covering Pittsburgh and the Chesapeake Bay.
The smoke may thin out during the day on Friday with cities like New York City seeing clearer conditions by Friday evening.
Major relief will move in by Monday when a cold front sweeps across the East, washing away much of the smoke in the air.
-ABC News' Daniel Amarante
New York City's Air Quality Health Advisory has been extended to Friday night.
While the AQI in New York City has been dropping significantly throughout the day, as of Thursday afternoon it registered at 178, which is still considered unhealthy.
Totals were over 400 in New York City on Wednesday. Levels under 100 are generally considered safe.
Learning will be remote on Friday for New York City public schools.
Air quality is measured by the Environmental Protection Agency’s air quality index (AQI), which ranges from 0 to 500. A higher level indicates a greater level of pollution and health concern.
Levels under 100 are generally considered safe.
Totals were over 400 in New York City on Wednesday.
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The White House has postponed the Pride celebration set to take place on the South Lawn on Thursday due to the unhealthy air quality.
The largest-ever White House Pride celebration will now take place on Saturday afternoon.
-ABC News' Justin Gomez
Thursday's MLB game in Washington, D.C., between the Nationals and the Arizona Diamondbacks has been postponed due to the air quality.
The makeup game will be held on June 22.
The National Zoo in Washington, D.C., is closed on Thursday as dangerous smoke moves through the capital.
"Today's air quality is extremely unhealthy," the Department of Energy & Environment warned. "Everyone should stay indoors as much as possible, especially sensitive groups such as children, elderly, pregnant women and people with heart or lung conditions like asthma and bronchitis."
Flights from the Northeast, Ohio and the Mid-Atlantic bound for the Philadelphia International Airport and New York City's LaGuardia Airport have been paused due to the smoke, the Federal Aviation Administration said Thursday morning.
The FAA cautioned, "We will likely need to take steps to manage the flow of traffic safely into New York City, DC, Philadelphia and Charlotte."
Waves of smoke will continue to move south Thursday from New York City to Philadelphia to Washington, D.C.
By Friday morning the AQI levels will drop for New York City. Smaller smoke plumes will linger from Detroit to Pittsburgh to D.C.
By Saturday and Sunday, the winds will begin to switch and blow smoke away from the U.S.
-ABC News' Max Golembo
Some school districts in New Jersey and New York announced closures or updated schedules for Thursday amid the heavy smoke in the area.
In New York, school has been canceled in the Freeport, Long Beach and Yonkers districts, according to New York ABC station WABC.
In New Jersey, school has been canceled in the Newark, Elizabeth, Union and Orange districts, WABC reported.
Officials at Elizabeth Public Schools said they'd attempted to continue a normal schedule by holding indoor recess on Wednesday.
"As the day advanced and the air quality worsened, we consulted with both health officials who updated their recommendation to close school buildings tomorrow, Thursday, June 8," Superintendent Olga Hugelmeyer said in a letter to parents.