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

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.

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.

CAL FIRE Sonoma-Lake-Napa Unit says several crews are at the site of a vegetation fire near Calistoga that has jumped to 60 acres. There is zero containment on the Napa County blaze that officials have dubbed as the Pickett Fire.