Crews battling a six-week-old wildfire lost ground overnight as it surged across about 13 square miles of arid brush, officials said Monday.

The fire's push into a densely forested wilderness area brought the total area blackened to about 148 square miles. It was expected to continue growing with triple-digit temperatures and low humidity predicted throughout the week, fire spokesman Joe Pasinato said.

"We'll most likely see some very aggressive fire behavior on the northeast side of the fire," Pasinato said. "Firefighters are predicting a very active day."

Elsewhere, the east entrance to Yellowstone National Park was closed Monday because of a Wyoming wildfire. Crews in Montana worked to mop up flames near a residential area before a change in the weather.

The California blaze, in the Dick Smith Wilderness and Los Padres National Forest, was just 44 percent contained, down from 68 percent the previous day, Pasinato said. The anticipated full containment date remained unchanged at Sept. 7. It started on July 4.

Controlled burns had blocked the fire from intruding deeply into a sparsely populated area south of the main fire area, he said. An evacuation order in that area was downgraded Sunday night to an evacuation warning, officials said.

A stretch of about 25 miles of the highway through Yellowstone's east entrance had been closed since Sunday afternoon because of a lightning-caused fire that had charred an estimated 12,000 acres, or about 18 square miles. The closure meant visitors headed to the park from Cody, Wyo., had to detour 29 miles through Montana.

Extremely active fire behavior was expected Monday, said Yellowstone spokesman Al Nash. The leading edge of the blaze was about 3 miles west of the park's east entrance, he said.

In Montana, firefighters worked to mop up flames near a residential area near Seeley Lake, northeast of Missoula, before an expected change in weather conditions that had subdued the blaze on Sunday.

"They do expect the fire to be active today as this inversion breaks," said fire information officer Tom Kempton.

The fire's spread during the weekend had led to the re-evacuation of about 300 residences in the area whose occupants had been allowed to return earlier. "Trying to control the areas (of the fire) that are closest to the populated areas has been a challenge," Kempton said.

Elsewhere in Montana, homes had been evacuated near a fire estimated at 8,500 acres near Livington, and about 30 homes, four church camps and a guest ranch had been evacuated near Big Timber because of a smaller fire.