Humidity and winds bedevil firefighters as wine country wildfires grow

Don’t let the lighter breeze fool you.

The recipe for fire remains at Atlas Peak in Napa County, as dry air continues to transform grass and vegetation to kindling.

The return of the windy, hot conditions Saturday once again put firefighters in defensive mode as they dealt with the sixth day of the most destructive, deadly fires in modern California history.

Strong winds kicked up overnight in the central Napa Valley region, causing some fires to spread and triggering evacuations in Sonoma and elsewhere, officials said.

But weather forecasters say it’s more than winds that are causing the danger.

“The biggest factor is the humidity. It’s been drying out the mountains,” said National Weather Service forecaster Steve Anderson. “It’s still going to be bone-dry out there overnight.”

Northerly winds, similar to Southern California’s Santa Anas, are expected to move across the region at about 15 mph overnight with some 25-mph gusts, Anderson said.

At the start of the fire last weekend, winds were blasting at more than 60 mph.Temperatures will drop into the mid-40s overnight Saturday, but a red flag warning won’t be lifted until 8 a.m Sunday at the earliest, Anderson said.

Temperatures are expected to hover in the mid-80s Sunday.

The wine country firestorms have killed at least 40 people and destroyed more than 5,000 structures.