In its latest update, Pacific Gas and Electric warned yesterday that up to 800,000 residents could lose power Wednesday morning. The extreme fire weather window is expected to last through Thursday afternoon, but the shutoffs could last for days after, as PG&E inspects its power lines.

The span of affected areas includes 34 counties in the northern Sacramento Valley and surrounding foothills, as well as Napa Valley and portions of the Salinas Valley and northern San Joaquin Valley. The update adds portions of Marin, Humboldt, Trinity, Santa Barbara and Kern counties to list. In Sonoma County, more than 80% of the businesses, nearly 21,000 in total, could lose power, according to officials.

Farmers and ranchers have now had four months to prepare backup generators for such a situation. PG&E surprised many when it shut off power to 22,000 customers in June in its first widespread “de-energizing” of power grids.

In recent years, state fairgrounds have taken over as emergency evacuation centers for pets and domestic livestock and state agencies have been training fair managers for emergency planning.

Beyond the red flag warning, the National Weather Service cautions that counties throughout the state will be experiencing dry, windy conditions and residents in rural areas should take wildfire precautions.