JUNCTION CITY, Calif. —Scattered showers forecast for California’s northern mountains Sunday are unlikely to extinguish wildfires that still threaten homes and could bring more lightning to the charred region, fire officials said.

The weather system is not expected to bring enough rain to have any effect on several huge blazes that have burned for nearly a month, said Pete Munoa, a spokesman for the California Department of Forestry and Fire Protection. A bigger concern is thunderstorms predicted to accompany the system.

But fire officials said cooler temperatures mean lightning strikes don’t pose as much of a threat as they did a month ago, when storms sparked nearly 2,100 fires that have burned almost 1 million acres.

“The weather pattern, if it holds the way it is now, we should be able to get a foothold around these fires,” Munoa said.

In the rural town of Junction City, residents were under mandatory evacuation orders for a third day Sunday as flames crept across the Shasta-Trinity National Forest. The month-old fire had spread to nearly 87 square miles by Sunday and was 49 percent contained.

All but 34 of the fires sparked after a lighting storm on June 20 have been contained around the state, leaving nearly 1,470 square miles of destruction in what officials call the largest fire event in California history. Fires consumed roughly 1,563 square miles in all of 2007.

A handful of residents near Dry Lake in Humboldt County were still under orders to stay away from their homes as another remote blaze spread to more than 18 square miles. That fire was 60 percent contained Sunday.

Authorities say most of California’s remaining fires are on remote federal forest land and pose little threat to homes.