Flash flood watch issued for Kincade fire burn zone

With a winter storm on its way from the Gulf of Alaska, the National Weather Service on Thursday issued a flash flood watch for the Kincade fire burn area in Sonoma County starting Friday afternoon, with to 2 to 4 inches of rain possible over a 12-hour period.

The watch - from 4 p.m. Friday to 4 a.m. Saturday - means conditions may lead to flash flooding, which is considered a “very dangerous situation,” the weather agency said.

Since heavy rains arrived last weekend, county officials have been warning of erosion in the area scorched by the 120-square-mile wildfire, with possible pollution of local waterways from ash swept by stormwater off scores of sites where buildings were burned to the ground.

Nearly 6 inches of rain have fallen at the Sonoma County Airport since Saturday, the Weather Service said. Rainfall from Friday through early Sunday could total 1.5 to 2.5 inches in North Bay valleys and 1.5 to 4 inches in the mountains.

Temperatures will remain cool through the weekend, dropping to the mid- to upper 40s overnight in Santa Rosa, said Ryan Walbrun, meteorologist for the Weather Service. Temperatures may reach as high as the upper 50s to 60 degrees, but there will be very little sun during the day.

Hourly rainfall rates could exceed a half-inch in an hour, leading to flash flooding or debris flows, the forecast said.

The agency also issued a wind advisory for the Bay Area from 10 a.m. Friday to 7 a.m. Saturday. Wind speeds could reach 15-30 mph Friday in the North Bay, Walbrun said. The wind will increase over the afternoon, with gusts reaching as high as 50 mph in higher elevations and along the coast.

Lighter rain is expected to continue all day Saturday in Sonoma County, with winds tapering off, Walbrun said. There will likely be some showers early Sunday morning, but Walbrun said the rain may stop later that afternoon.