The National Weather Bureau has issued a red flag warning for wildfires for much of Northern California today through Wednesday as forecasters predict 40 mile per hour winds in the Sacramento Valley and the North Coast, and 50 mile per hours winds in the Sierra Foothills. The weather service also warned of low humidity between 20 and 30% along with Temperatures rising to the mid 90a s. The weather servicea s previously issued fire weather watch was upgraded shortly after Pacific Gas and Electric Co. said Saturday that it may pre-emptively shut off power in the region. As many as 67,000 PG&E customers in Butte, El Dorado, Nevada, Placer, Sutter and Yuba counties could be affected by a power shutoff.