Mother Nature is providing some help in the battle against northern Ontario's forest fires. Rain has dampened the earth and slowed the spread of some blazes. But the ultimate effect of the fortuitous weather is yet to be seen.

Three days of rain, heavy cloud and high humidity have covered most of northern Ontario, allowing firefighters the opportunity to wrest control over the 30-plus forest fires burning in the area.

"With that kind of weather you aren't seeing rolling blowing flames," said Deb MacLean, a spokesperson for the Ministry of Natural Resources. "You're seeing smoldering, little puffs of smoke, maybe some flames. This is a temporary reprieve."

On Friday, sun and cloud are expected to return to much of northern Ontario, drying up the earth and raising temperatures.

"It is a good test because we'll see how far we've made it in fighting the fires," said MacLean. "Will it put us back into the same jackpot that we were in earlier in the week? That will remain to be seen."

In Sioux Lookout, the northwestern community where a 300-square-kilometre fire raged, heavy rains allowed firefighters to keep the flames at bay, but not to extinguish them.

"We've still got rain but it's still a pretty big fire and it's going to take a lot more than the rain to put it out," Fire Commander Richard Rivet told CTV News.

But thunderstorms passing through the region have proved a mixed blessing. Rainfall isn't quenching new fires sparked by lightning strikes.

Smoke continued to pose a threat to nearby towns. The Northwestern Health Unit said people should shut their windows, turn off air exchangers, and limit the use of air conditioners and outdoor activities.

In the Wawa district, where the largest fire covers 200 square kilometres, foggy conditions grounded water-bombers, but bulldozers were able to dig trenches around the flames, Dicaire said.

As of Thursday afternoon, there were 38 fires consuming 2,432 square kilometres of forest in Ontario. At this time last year, there were 191 fires burning over 249 square kilometres.

With reports from CTV's Jill Macyshon and the Canadian Press