A heat advisory for the area is in effect until 9 p.m. Saturday. Temperatures in Calistoga are expected to reach a low of around 59 degrees Friday night and a high of near 91 degrees on Saturday, with 5 to 7 mph winds. The chances of dry lightning are low but “not zero,” the weather service said in its forecast discussion.

The Pickett Fire erupted in Napa Valley on Aug. 21 forcing evacuations for many in the area and threatening people, structures and wineries.

The Pickett Fire near Calistoga nearly doubled in size Thursday night, reaching 2,131 acres with no containment, according to Cal Fire.

The Pickett Fire near Calistoga in Napa County expanded to 3,993 acres Friday night as firefighting efforts continued with night-flying helicopters and containment held at 7%, Cal Fire said.

As the Pickett Fire outside Calistoga grew to 2,133 acres, Napa County authorities ordered evacuation from a fourth Upvalley area as hundreds of firefighters battled the blaze.