NEW YORK — Wildfires burning in Canada continue to create poor air quality conditions in the U.S. as the smoke makes its way south.

Hazy skies, low visibility and poor air quality will be present in most of the Northeast and the Midwest and even as far south as the Carolinas.

Air quality alerts have been issued in 13 states, and the worst air quality in the U.S. on Wednesday was in New York from Syracuse to Binghamton.

Smoke plumes are now extending along the East Coast, with smoky skies lingering into the Ohio Valley.

Air quality is currently deemed "unhealthy" for millions of residents. With these ratings, all individuals, not just sensitive groups, should limit time spent outdoors.

A very dense area of smoke over upstate New York has swept down across New Jersey, New York City and southern New England.

Large cities with the lowest air quality on Wednesday include New York City, Washington, D.C., Philadelphia and Columbus, Ohio, a map by AirNow, a website that publishes air quality data, showed. On Tuesday, New York City had the worst air quality rating in the world due to the smoke.

Another large and dense plume of smoke is making its way down across parts of the Northeast on Wednesday, delivering a one-two punch for cities like New York City and Philadelphia, which will worsen the air quality yet again -- perhaps even more dangerous than conditions were on Tuesday. That batch of very dense smoke will push down across the Northeast throughout the day on Wednesday, giving some relief to New England and the Midwest but extending the smoke further south, toward Atlanta and Huntsville, Alabama.

By Thursday evening, conditions will likely improve east of the I-95 corridor and around New York City but will worsen in western New York, Pennsylvania and West Virginia, as the winds shift, forecasts show.

At-risk populations, such as young children, the elderly or those with lung and heart disease, should especially avoid the outdoors, according to the advisories.

A storm system approaching the East Coast this weekend will then shift winds to a more southerly direction, easing the effects of the wildfire smoke.

The smoke originated from wildfires in Quebec, where more than 160 forest fires are currently active. Some of the fires in the region were ignited by lightning strikes, according to NASA. Unusually dry and warm weather has fueled the fires.

The intensity of the fires has exceeded the capacity of water bombers, Quebec's wildfire prevention agency announced on Monday, CTV reported.

Firefighters are currently unable to get the wildfires under control, François Legault, a member of the Canadian parliament serving Quebec, told reporters during a news conference on Monday. Firefighters in other provinces are unable to assist because they are battling their own fires but an additional 200 firefighters are traveling from France and the U.S., Legault said.

The number of wildfires in the country has grown past 400, officials said, and conditions are not forecast to improve in the coming days.

Northern U.S. states have been under the haze of the migrating smoke since early-season wildfires began to spark in mid-May.

Air quality alerts were issued for all of Montana and parts of Idaho, Colorado and Arizona due to wildfires in Western Canada.

Wildfires burning last week near Halifax, Nova Scotia, created hazardous air quality ratings in many of the regions affected by the wildfires currently burning in Quebec.

There is also an elevated fire danger from northern Michigan to Pennsylvania and New Jersey, with red flag warnings in effect for some areas. If any fires spark, they could easily spread due to the very dry conditions and gusty winds. Lightning from isolated thunderstorms in Pennsylvania and New Jersey could be a source of new wildfire ignition.

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