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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