ANTA ROSA, Calif. — The wind known as the Diablo has picked up again, the air is dry, there is no rain in sight and the killer wildfires ravaging Northern California’s wine country remained almost completely uncontained Thursday morning. Officials warned that some of the big fires could merge, even as new blazes erupted, and thousands of people have been told to prepare to leave their homes — if they haven’t already. Evacuations continue, including one order covering the entire city of Calistoga in Napa County. …“These destructive winds, along with millions of trees weakened by years of drought and recent renewed vegetation growth from winter storms, all contributed to some trees, branches and debris impacting our electric lines across the North Bay,” she said. …Officials with the California Department of Forestry and Fire Protection (Cal Fire) said they have yet to determine the cause of the fires.