SAN FRANCISCO (CBS SF) — The Bay Area office of the National Weather Service on Tuesday morning upgraded a Fire Weather Watch for the North and East Bay to a Red Flag Warning for the region.

The Red Flag Warning has been issued for the interior North Bay Mountains and East Bay Hills and Diablo Range starting at 11 p.m. Tuesday through Wednesday afternoon.

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The winds coupled with extremely low humidity are combining for critical fire weather conditions across those regions.

Weather officials said there was minimal risk for coastal Sonoma and Marin counties and the Santa Clara Mountains.

“The greatest risk for this red flag warning is really the northeastern portion of the Napa Mountains. That’s where we could see gusts of up to 55 miles per hour, “said Cal Fire Assistant Deputy Director Daniel Berlant.

Despite the drain on Cal Fire resources from the many fires already burning across the state, Berlant said that the agency was ready in case something happened in the Bay Area Tuesday night.

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“We’re definitely preparing with extra resources and extra firefighters on the ready. Across much of the North Bay and down into the East Bay, we need those residents to be prepared,” Berlant said.

He also stressed the importance of residents being ready in case something happens in their region.

“We really need everybody tonight to be prepared; to know what they would take if a wildfire breaks out in their area and they have to evacuate,” Berlant said.

The dangerous weather conditions led PG&E to expand its possible Public Safety Power Shutoffs planned for Tuesday evening. The utility may cut off power for thousands of customers in 18 Northern California counties on Tuesday.

Some 48,000 ratepayers received notification on Monday that the agency may shut off power due to the heightened wildfire danger.

PG&E says the planned Public Safety Power Shutoffs would begin on Tuesday evening and last through Thursday afternoon.

According to PG&E meteorologists, portions of the Sierra Nevada foothills, North Coast, North Valley and North Bay mountains may see “sustained winds of up to 40 mph, gusting higher in foothills and mountains,” and that has prompted state weather officials to issue a “high fire risk warning.”

Most of the shutoffs will be concentrated in Butte and Shasta counties. Residents in Colusa, Glenn, Humboldt, Lake, Lassen, Mendocino, Napa, Nevada, Plumas, Sierra, Solano, Sonoma, Tehama, Trinity, Yolo and Yuba may also be impacted.

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Customers can look up their address at pge.com/pspsupdates to see if their home or business will be impacted.