SAN FRANCISCO (KGO) -- Our helicopter was overhead as the huge plume of smoke from the Kincade Fire continued spreading over Sonoma County.
ABC7 News Meteorologist Lisa Argen says smoke from wildfire prompted officials to call a Spare the Air alert for Thursday. She notes that shifting winds may cause the smoke to blow directly over much of the region.
The Kincade Fire exploded in size early Thursday amid dangerous winds that prompted the state's largest utility to impose electrical blackouts to prevent fires.
RELATED: Shifting winds may blow smoke from Sonoma County wildfire over parts of Bay Area
Authorities ordered the entire community of Geyserville to evacuate after the fire in the Sonoma County wine region north of San Francisco grew to more than 15 square miles. The town has about 900 residents and is a popular stop for wine country tourists.
The cause of the blaze was not yet known, but wildfire risk was extremely high as humidity levels plunged and winds gusted up to 70 mph.
Get the latest developments on the Kincade Fire here.
The Associated Press contributed to this report.
Kincade Fire: SKY7 captures huge plume of smoke from Sonoma County wildfire