The National Weather Service issued a red flag warning Thursday for the North Bay hills, with winds gusting as high as 30 mph through 5 p.m.

Winds will generally be 10 to 20 mph at elevations of 1,000 and up, said Charles Bell, a meteorologist.

Lighter winds are expected after 5 p.m. and overnight in the hills and valleys in Napa and Sonoma counties, he said.

Around mid-afternoon Friday, northerly winds are expected to pick up, blowing 10 to 20 mph in valleys and 20-30 mph in the hills, with isolated gusts at 40 mph or more, through Saturday evening, Bell said.

Lighter winds are expected Sunday and dry conditions will prevail through the weekend.