WEED, Calif. (AP) — Hundreds of firefighters faced more hot and dry weather on the lines of big wildfires in Northern California on Thursday.

The extraordinary Pacific Northwest heat wave that reached down into the upper reaches of California was slowly receding but only slight cooling was expected before temperatures trend back up heading into the weekend.

The Lava Fire in the shadow of volcanic Mount Shasta grew to 30.7 square miles (79.5 square kilometers) and was 19% contained but all evacuation orders for communities north of the city of Weed remained in effect, the Shasta-Trinity National Forest said.

The steep, rocky terrain was challenging the nearly 1,300 firefighters on the lines of the blaze, which was ignited by lightning last week.

To the northeast, a fire that broke out Monday in the Klamath National Forest and forced evacuations covered 12.7 square miles (32.9 square kilometers) and was just 6% contained. The fire was expected to advance north toward Oregon. Its cause remained under investigation.

Evacuations were also in effect to the south where a new fire erupted Wednesday afternoon and spread rapidly in the Shasta Lake area north of the city of Redding. The fire was estimated at more than 4 square miles (10.3 square kilometers) early Thursday.