Canadian wildfire smog still choking areas of U.S. but expected to diminish

June 15 (UPI) -- Smog from wildfires raging in Canada is once again making its way south of the border into the Northeast and beyond, causing air quality warnings Thursday.

The smoke is expected to be thickest in the Northeast on Friday but will not approach levels seen last week.

East Coast cities such as Boston and New York will once again see the skies cloud over.

St. Paul, Minn., had the lowest air quality in the country on Wednesday, the worst it has seen in 40 years. It should dissipate late Friday.

The U.S. National Weather Service had issued air quality warnings across five Midwest states as of Thursday afternoon, including Missouri and Kansas.

Air quality levels in parts of Minnesota reached "unhealthy" levels on Thursday.

Rain in the forecast for Saturday should help alleviate the situation.

"The big takeaway is that it will be nowhere near as bad," Fox Meteorologist Brian Mastro told the New York Post in an interview Thursday.

There are currently more than 450 active wildfires burning in Canada, having scorched more than 5.4 million acres. Of those fires, nearly 220 are deemed to be out of control, according to Canadian Interagency Forest Fire Center.

Fires in the Canadian provinces of Ontario, Quebec and Nova Scotia are affecting the U.S. Northeast, while fires in the prairie province of Alberta are contributing to smoke in the Midwest.