Canada's Alberta blanketed by smoke as wildfire-battle continues

May 17 (Reuters) - Smoke blanketed the skies over much of Alberta on Wednesday as firefighters from Canada and the United States battled raging wildfires that have prompted evacuations, disrupted rail service and shuttered energy production in Canada's main oil-producing province.

Hot and dry conditions have triggered an intense start to wildfire season in Alberta. Authorities had lifted some evacuation orders on Tuesday, yet nearly 20,000 people have been forced out of their homes.

On Wednesday, consultancy firm Rystad Energy said nearly 2.7 million barrels per day (bpd) of Alberta oil sands production in May is at risk in "very high" or "extreme" wildfire danger rating zones.

Of estimated May production volumes, about 60% are currently subject to extreme wildfire danger levels, with the remaining 40% subject to very high danger, Oslo-based Rystad said.

A cold front this week eased historically high temperatures, but conditions remain very dry and windy, with no rain expected until next week, according to Environment Canada's weather department.

Wildfire smoke has covered a large part of Western Canada. Air quality in places including Edmonton and Alberta has deteriorated to category 10+, the worst level on Environment Canada's Air Quality Health Index, indicating "very high risk."

Alberta goes to the polls on May 29.

Winds, that have also carried smoke to neighboring provinces are expected to weaken Wednesday night, but any improvement in air quality will probably be temporary, said Jesse Wagar, a meteorologist with Environment Canada.

"There is some improvement expected, but it'll likely be short lived just because how many fires there are ... we're likely to have smoke moving from really any direction," Wagar said.

More than 2,500 firefighters, including personnel from Canadian and U.S. agencies as well as the Canadian army, were battling the wildfires in Alberta. The province has also issued a plea to some 20,000 public servants, encouraging anyone with firefighting experience to volunteer to battle the blazes, the Toronto Star newspaper has reported, citing an email send to employees.

The wildfire activity has also caused rail disruptions, but the impact is unlikely to have credit implications for the Canadian grain handling sector, said Moritz Steinbauer, vice president of diversified industries at ratings agency DBRS Morningstar.