DES MOINES, Iowa (AP) -- A haze blanketed much of the Midwest on Tuesday as strong winds carried smoke from forest fires in Canada thousands of miles to the south, prompting health warnings in at least two states.
Smoke from wildfires in northern Saskatchewan was blowing as far south as Tennessee, with a thick haze extending through much of North Dakota, South Dakota, Minnesota, eastern Nebraska, Iowa, Illinois and Missouri.
"There's a ton of smoke from Canada across the northern Plains," said Bill Borghoff, a weather service forecaster in Chanhassen, Minnesota. "The strong jet stream makes for a perfect setup to bring all this smoke to the south."
The smoke is from dozens of fires burning in Saskatchewan, fed by drought and high temperatures.
The smoky conditions caused county health departments in Des Moines, Iowa, and Omaha, Nebraska, to issue warnings, urging people to refrain from exercising outside. People with heart or lung diseases and the elderly are at increased risk of health problems that would require hospital emergency room visits, officials said.
Brad Fillback, a weather service forecaster in Johnston, Iowa, said the smoke is likely reducing daytime temperatures by a few degrees but allowed for less cooling at night.
"It's acting a bit like clouds," he said.
The smoke should shift eastward by Thursday, first spreading toward the Great Lakes but later reaching as far east as New England.
As it moves east, the smoke should be less dense, as high-altitude winds cause it to "fracture," Borghoff said.
It's unclear how long the fires in Canada could burn, and Borghoff said wind conditions could bring more smoke into the Midwest in a couple weeks.