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.

According to Cal Fire, the blaze had reached 4,690 acres as of Saturday, and was 7% contained, with crews working overnight to keep the fire within control lines.

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 in Napa County has swelled to over 2,100 acres, remaining 0% contained as firefighters face challenging conditions.

The Pickett Fire doubled in size overnight as firefighters struggled to reach the remote, steep rugged terrain where it was burning in the North Bay, authorities said.