SAN FRANCISCO (CBS SF) — Pacific Gas and Electric technicians have commenced a Public Safety Power Shutoff (PSPS) Tuesday evening across a wide swath of Northern California, including the North Bay and East Bay.

The PSPS will affect an estimated 51,000 customers, the utility said.

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The scope of the expected power shutoffs has been expanded as the region is under a Red Flag Warning for extreme fire conditions because of dry conditions and gusty winds that have continued to fuel wildfires in the region. At least 18 Northern California counties may lose power, PG&E said, with most of the shutoffs concentrated in Butte and Shasta counties.

On Tuesday night, the western side of Calistoga was in the dark as the town coped with dangerous fire conditions.

Rancho de Calistoga is a mobile home park for seniors and it’s been hit hard by the outages. Residents had hoped they wouldn’t be left in the dark again.

“Here we go again,” said resident Renate Schreiner.

She and her neighbors are very familiar with Public Safety Power Shutoffs.

“I thought it would be later in the season but with this weather and dryness. I’d rather take that than the fire. Believe me,” said Schreiner.

While a large microgrid provides power to the the City of Calistoga east of the Napa River, those to the west have lost power. It went off earlier than expected around 6:30 pm and according to PG&E, the PSPS is expected to last until Wednesday afternoon.

For Herb Welch, this means a couple of sleepless nights without power to operate his medical equipment.

“I have to have power so I don’t sleep without that so basically I’m up all night,” he explains.

Neighbor Daniel Sund adds, “It’s real disappointing but hopefully this will make a big difference.”

Sund is talking about an emergency back up generator. The City of Calistoga used grant funds to buy the generator to provide power to roughly 120 units in this mobile home park. Residents are crossing their fingers it will be online soon and PSPS will be a thing of the past for them.

“This will be the last summer we have to deal with this I hope,” said Herb Welch.

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In the greater Bay Area, planned outages could total more than 13,000 beginning between 6 and 8 p.m. mostly in Napa and Sonoma counties, with other outages planned in Marin, Solano, Contra Costa, Lake and Mendocino counties.

PG&E said should the outages occur, restoration was expected between 10 a.m. and 2 p.m. Thursday.

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PG&E estimated there were about 4,000 people without power in Napa County and it is also affecting those in Solano and Sonoma counties as well.

Contra Costa County announced that there would be a PG&E Community Resource Center at St. Bonaventure Catholic Church in Concord started Tuesday night at 5 p.m.

On Tuesday, the National Weather Service 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. Gusty winds up to 55 mph are forecast out of the north and northeast, particularly in the northeast Napa Mountains.

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.

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.”

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Andrea Nakano contributed to this story.