THE LATEST: Nov. 20, 12:20 p.m.: Due to a shift in weather conditions, Pacific Gas and Electric announced it was scaling back the number of customers impacted by a power shut-off that began Wednesday morning.

The utility said in a statement Wednesday afternoon that power will not be cut to 83,000 customers originally expected to go in the dark. Shut-offs are canceled in El Dorado, Nevada, Placer, Sierra, Yuba and west Sonoma counties.

PG&E said it turned off the power Wednesday morning for approximately a total of 48,000 customers in portions of Colusa, Glenn, Lake, Mendocino, Napa, Shasta, Solano, Sonoma, Tehama and Yolo counties. The original scope of the shutoff was 300,000 customers, but this number has been incrementally reduced as the weather forecast indicated less extreme fire conditions.

Portions of eastern Sonoma County lost power Wednesday morning and county officials shared on Twitter that PG&E will "start inspections and re-energization around 8 a.m. Thursday. They hope to have power back on for all customers by 10 p.m."

Napa County shared on Twitter that power started going out in some areas at 7 a.m. A timeline for when the lights will go back on in Napa hasn't been shared.

UPDATE: Nov. 20, 7:50 a.m.: Pacific Gas and Electric began cutting power at 7 a.m. for customers in Solano, Napa and Sonoma counties to reduce the risk of equipment becoming damaged and sparking a wildfire during a wind event.

PG&E had originally announced deliberate blackouts in eight Bay Area counties, but due to changes in the weather forecast, Alameda, Marin, Santa Clara, Contra Costa and San Mateo counties were taken off the list.

PG&E spokesperson Katie Allan said as of 7 a.m. the plan is to cut power to 11,183 customers in Napa County, 81 customers in Solano County and 19,265 customers in Sonoma County. In total, 29,780 Bay Area customers — or approximately 89,340 people if you consider the average of three residents per household — will be impacted.

The process can take several hours and some people who are scheduled to lose power may not have seen the lights go out right at 7 a.m.

The preventative outages come as onshore winds have developed at higher elevations in certain locations around Northern California. PG&E power safety shut-offs also are underway in 15 other Northern California counties outside the Bay Area: Amador, Butte, Colusa, El Dorado, Glenn, Lake, Mendocino, Nevada, Placer, Plumas, Shasta, Sierra, Tehama, Yolo and Yuba. Across all 18 counties, up to 150,000 customers (or 450,000 people) will be affected.

National Weather Service forecaster Scott Rowe said winds had developed in the North Bay mountains and East Bay hills early Wednesday.

A 71 mph gust was recorded on Mount St. Helena at 5:51 a.m. While the winds are mostly blowing at elevations above 1,000 feet, Rowe said Napa Valley is experiencing sustained winds of 28 mph. In the East Bay, Mount Diablo was knocked with a 53 mph gust.

Winds are forecast to decrease slightly in the afternoon but will pick up after sunset before subsiding Thursday morning.

Low relative-humidity values are another factor in extreme fire weather and on Tuesday low-pressure system swept the region, carry a mass of moist air and some locations in the South Bay and North Bay reported brief rain showers. The atmosphere was high in moisture Wednesday morning, but humidity values are expected to drop rapidly through the day as temperatures warm up and desiccating winds continue to blow.

"Relative humidity is at 62 percent on Mount St. Helena," said Rowe at 6:30 a.m. "We'll see those relative-humidity levels fall as the day progresses, probably below 30 percent."

Rowe added, "While the rain certainly helps with fire weather concerns, we usually look for more significant weather to dampen fuels [vegetation] and reduce wildfire risk."

PG&E meteorologist Scott Strenfel said in a press conference Tuesday night that 2019 has been one of the driest starts to the rainy season in 100 years.

If you look at precipitation totals for cities across Northern and Central California, some have observed no precipitation as of [Oct. 1]," said Strenfel. "As an example, a climate station in Napa, which is called the Napa Sate Hospital Fire Station, has not recorded any measurable precipitation since September 15 and the last time that occurred was 1905."

When the winds calm on Thursday morning, PG&E will begin inspecting equipment and turning power back on.

"Our goal is to restore most of our customers by end-of-day Thursday," Allan said.

Amy Graff is a digital editor for SFGATE. Email her at agraff@sfgate.com.