The haze blanketing Smithfield this week isn’t just fog and may stick around for a few days, according to the National Weather Service’s Wakefield station.

Smoke from Canadian wildfires burning more than 500 miles away reached Hampton Roads on Wednesday, prompting the NWS and Virginia Department of Environmental Quality to issue a “unhealthy” air quality alert Thursday morning that will remain in effect through midnight.

“Everyone should avoid prolonged or heavy outdoor exertion,” the NWS warning states. “Those with respiratory and/or heart ailments may experience more serious health effects.”

Visibility and breathability could get “pretty nasty” by this afternoon, said NWS Meteorologist Ryan Rogers.

A closed low-pressure weather system is circulating air counter-clockwise, Rogers said, providing a direct route south for particulates from fires in the Canadian province of Quebec.

“Once it gets into the atmosphere, it travels very quickly,” Rogers said.

According to the U.S. Environmental Protection Agency, particulates, or PM 2.5, refer to smoke or soot particles with diameters 2.5 micrometers or smaller, which are small enough to cause health problems if inhaled. A human hair, by comparison, is about 70 micrometers thick.

The U.S. Air Quality Index, which measures ground-level ozone and particulates in the atmosphere on a zero-to-500 scale, was reporting a “moderate” AQI of 84 in Smithfield as of 11 a.m. Thursday. An AQI of 50 or below is considered “good” or “green,” while a value of 100 or higher is considered “unhealthy” or “code red.” Smithfield is expected to reach a code red score of 151 by Thursday afternoon.

Today should be “the worst of it,” Rogers said, but he predicted the area could still see “code orange” pollution levels on Friday, which would range from 100 to 150 on the AQI scale.

Ground-level ozone, the other component of the AQI, refers to the colorless gas formed by the reaction of sunlight with industrial and vehicle emissions, and typically occurs in hot, dry weather, according to the DEQ. Smithfield’s ozone levels are expected to stay below 50 or “green.”

According to Associated Press reporting, Canadian officials are predicting this spring and summer to be the nation’s worst wildfire season ever. Canadian officials have asked other countries for help in battling more than 400 separate wildfires, about 100 of which were deemed “out of control” as of Wednesday in Quebec.

The Virginia High School League’s “Spring Jubilee” June 9 semifinal games in Spotsylvania County, where Smithfield High School’s baseball team and boys and girls soccer teams are to compete, were still on as of Thursday. VHSL staff have “closely monitored the Air Quality Index” and “the forecast does not show those areas in red for Friday and Saturday,” states a June 8 VHSL news release.

Editor’s note: This story was updated at 2:29 p.m. on June 8 with information on how the smoke will affect Smithfield High School’s state semifinal games.