The Statue of Liberty sits behind a cloud of haze on Tuesday in New York City. According to data from the National Oceanic and Atmospheric Administration, wildfire smoke from the west has arrived in the New York-New Jersey area, creating decreased visibility and a yellowish haze in many areas.

PHILADELPHIA — Shrouds of smoke from wildfires in the Pacific Northwest again are congesting the skies over much of the nation — and they are forecast to persist at least well into Wednesday.

While smoky haze from distant wildfires isn’t all that unusual, said Tom Kines, senior meteorologist with AccuWeather Inc., “to have it this thick, it doesn’t happen very often.”

Air-quality alerts were in effect on both sides of the Delaware, with health officials advising those with heart or lung issues to eschew strenuous outdoor activity. However, the fact that the smoky veil will remain so high in the atmosphere should mitigate the health impacts, said Kines.

Canadian fires were concentrated Tuesday along the British Columbia-Washington border, and the massive “Bootleg Fire” has engulfed close to 400,000 acres of woodlands in south-central Oregon, forcing evacuations, the Northwest Interagency Coordination Center reported.

Prevailing upper-air winds were exporting the smoke all the way to the Atlantic seaboard and were likely to continue to do so Wednesday, according to the National Centers for Environmental Prediction.

The smoke was stacked in a roughly two-mile layer, five to seven miles above the surface, said Patrick O’Hara, meteorologist with the National Weather Service in Mount Holly.

If you think you’re smelling smoke, you’re not necessarily hallucinating: A subtle odor might be detectable on occasion, he said, as some of the particles could mix down close to the surface.

Wildfire smoke made the 2,500-mile journey to the East Coast as recently as two weeks ago, but it was far less substantial than this refill.

And while the extent of the Bootleg wildfire and the smoke plumes has been impressive, it evidently hasn’t had the impacts of recent deadly fires in more-populated areas.

Oregon is one of the nation’s largest states — bigger than the combined areas of Pennsylvania, New Jersey, Delaware, Maryland, and West Virginia — and has vast unpopulated regions. New Jersey has 30 times more people per square mile than Oregon.

The smoke likely was shaving a degree off the temperature in some East Coast cities, said Kines, and it might be adding a dash of drama to sunsets.

Kines said a front approaching should clear the region late Wednesday, and ultimately broom away the smoke.