While millions of Northeastern U.S. residents sought shelter from the historically-bad air quality resulting from smoke drifting south from Canada’s wildfires, flight operations at area airports were also affected due to low visibility.

The FAA issued ground stops for flights destined for Philadelphia International and New York LaGuardia airports on Wednesday and today issued ground delay advisories for aircraft bound for LaGuardia and Newark Liberty International Airport until this evening due to limited visibility. A spokesperson from the Port Authority of New York & New Jersey told AIN that business aviation hub Teterboro Airport has only experienced minor delays in operations due to volume.

According to some forecasts, smoky conditions could persist through the weekend and the plume could move further south and impact areas such as Washington, D.C.

The FAA noted that the smoke is causing widespread delays on flights—on average more than 30 minutes—throughout the U.S. air traffic control system and warned it “will likely need to take steps to manage the flow of traffic safely into New York City, D.C., Philadelphia, and Charlotte [North Carolina] due to reduced visibility from wildfire smoke."