Smoke from Canada wildfires drifts into US

Smoke from dozens of raging wildfires in western Canada has drifted south into the United States and prompted the states of Colorado and Montana to issue air quality alerts.

Colorado's Department of Public Health and Environment released alerts and advisories for Saturday afternoon through Sunday afternoon for much of the eastern half of the state, including Denver.

It warned that air quality may be unhealthy during that period.

“People with heart or lung disease, older adults, and children should avoid prolonged or heavy exertion; everyone else should reduce prolonged or heavy exertion,” the department said.

Particle pollution led the air quality index along parts of the Front Range to reach 168 on Saturday, the department said. A reading between 151 and 200 indicates unhealthy conditions that can affect sensitive groups as well as some members of the general public.

An air quality alert was also in effect on Saturday in Montana, with the greatest smoke concentrations in central and eastern parts of the state, according to the Department of Environmental Quality.

Utah's Department of Environmental Quality said on Friday that it was starting to see the smoke on its monitors in northern and eastern parts of the state. It urged residents to avoid outdoor exertion in areas with visible smoke or haze.

The smoke created widespread haze across Idaho earlier in the week, according to its Department of Environmental Quality.

The fires in Canada have been burning mostly in the province of Alberta, where thousands of residents have evacuated and regional officials have issued state of emergency alerts.

There have also been fires in British Columbia.

In Calgary and Edmonton, the two biggest cities in Alberta, the health impact was determined to be of “very high risk” on Saturday by the Canadian government's Air Quality Health Index.

Cool rain to make 'big difference'

A cool rain is coming — the first in weeks — and Canadian authorities said they hope it makes a "big difference" in Alberta, the western province battling wildfires after a hot, dry start to a holiday weekend.

Officials were on high alert after fires displaced tens of thousands of people and scorched more than 800,000 hectares of forests and grasslands in recent weeks.

The Alberta Wildfire agency's Christie Tucker said a few "scattered showers and thunderstorms" had been spotted in parts of the province earlier in the day.

"As we look ahead to the week, our forecasters are tracking a front moving into the province from tomorrow [Sunday], which should bring much-needed cooler temperatures, humidity and even rain," she told a news conference.

That should last "a few days," she said.

"A lot depends on where exactly that rain falls... But in the area we're expecting it, it is forecast to make a big difference" for more than 2,500 firefighters battling 87 blazes — including 23 out of control — as of late Saturday.

Officials would prefer a longer, steady rain that soaks into the forest.

"That will help us more than a short burst that would bring lightning and could spark a new wildfire," she said.

Over 10,000 Albertans remained under evacuation orders on Saturday, down from a peak of almost 30,000.

Cyndee Evans, head of the Alberta Emergency Management Agency, said the wildfire situation "remains volatile."

In recent years western Canada has been hit repeatedly by extreme weather, the intensity and frequency of which have increased due to global heating.