Southern California Edison shut off power to 12,900 customers in Los Angeles, San Bernardino, Ventura and Kern counties on Thursday in an effort to lower wildfire risks amid the high fire danger brought on by the arrival of Santa Ana winds.

The number was an increase from 4,700 the utility company gave Thursday morning.

The power provider did not give a breakdown about how many customers in each county were affected, though it maintained that nearly 174,000 remain at risk of the same fate. Many of those affected are in foothills and mountainous areas.

Powerful winds whipped throughout Southern California. The strongest gust recorded on Thursday reached 72 miles per hour near CSU San Bernardino. Winds peaked at 65 miles per hour at Pleasants Peak in the hills separating Orange and Riverside Counties. Gusts moved as fast as 35 miles per hour in the western part of the San Fernando Valley in Los Angeles County, according to the National Weather Service.

Combined with the warmer temperatures and lower humidity is a recipe for wildfires. The low humidity is caused by cold air and a drying-out effect that occurs when the gusts blow across mountain slopes.

Palm trees are obscured by dust as high winds blow through Fontana on Thursday, Oct 10, 2019. (Photo by Will Lester, Inland Valley Daily Bulletin/SCNG)

Strong Santa Ana winds blew across power lines causing them to arc and transformers to explode. Power was out for street signs, businesses and residents along Devonshire St. from Topanga Canyon Blvd. to Variel Ave. on Thursday, October 10, 2019. (Photo by Dean Musgrove, Los Angeles Daily News/SCNG)

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Strong Santa Ana winds blew across power lines causing them to arc and transformers to explode. Power was out for street signs, businesses and residents along Devonshire St. from Topanga Canyon Blvd. to Variel Ave. on Thursday, October 10, 2019. (Photo by Dean Musgrove, Los Angeles Daily News/SCNG)

Strong Santa Ana winds blew across power lines causing them to arc and transformers to explode. Power was out for street signs, businesses and residents along Devonshire St. from Topanga Canyon Blvd. to Variel Ave. A sign is posted on a Chatsworth strip mall business on Thursday, October 10, 2019. (Photo by Dean Musgrove, Los Angeles Daily News/SCNG)

Strong Santa Ana winds blew across power lines causing them to arc and transformers to explode. Power was out for street signs, businesses and residents. Dan Rosen stands in the doorway of his Edward Jones investment office in Chatsworth on Thursday, October 10, 2019. (Photo by Dean Musgrove, Los Angeles Daily News/SCNG)



Strong Santa Ana winds blew across power lines causing them to arc and transformers to explode. Power was out for street signs, businesses and residents. The Edward Jones investment office posted a sign at their Chatsworth office on Thursday, October 10, 2019. (Photo by Dean Musgrove, Los Angeles Daily News/SCNG)

Strong Santa Ana winds blew across power lines causing them to arc and transformers to explode. Power was out for street signs, businesses and residents. Caution tape crosses a closed Devonshire St. at Owensmouth Ave., east of Topanga Canyon Blvd. on Thursday, October 10, 2019. (Photo by Dean Musgrove, Los Angeles Daily News/SCNG)

Strong Santa Ana winds blew across power lines causing them to arc and transformers to explode. Power was out for street signs, businesses and residents. A LAPD vehicle blocks a closed Devonshire St. at Owensmouth Ave., east of Topanga Canyon Blvd. on Thursday, October 10, 2019. (Photo by Dean Musgrove, Los Angeles Daily News/SCNG)

Strong Santa Ana winds blew across power lines causing them to arc and transformers to explode. Power was out for street signs, businesses and residents. Two LAPD officers stand on a closed Devonshire St. at Owensmouth Ave., east of Topanga Canyon Blvd. on Thursday, October 10, 2019. (Photo by Dean Musgrove, Los Angeles Daily News/SCNG)

Santa Ana winds blow through a horse stable in Chatsworth next to Stoney Peak Park on Topanga Canyon Blvd. on Thursday, October 10, 2019. (Photo by Dean Musgrove, Los Angeles Daily News/SCNG)



Ivo Gough Eschrich, a fire watch volunteer, calls in the wind speed he measured at his location along Santiago Canyon Road just west of Silverado Canyon on Thursday morning as dry Santa Ana winds began to blow and gust in eastern Orange County. Fire watch volunteers spread out throughout the area to keep an eye out for possible fires and fire hazards on Thursday, October 10, 2019. (Photo by Mark Rightmire, Orange County Register/SCNG)

A red fire alert flag flies at the intersection of Santiago Canyon Road and Silverado Canyon on Thursday morning as dry Santa Ana winds began to blow and gust in eastern Orange County. Fire watch volunteers spread out throughout the area to keep an eye out for possible fires and fire hazards on Thursday, October 10, 2019. (Photo by Mark Rightmire, Orange County Register/SCNG)

High winds blow dust and tumbleweeds across Victoria Street in Fontana on Thursday, Oct 10, 2019. (Photo by Will Lester, Inland Valley Daily Bulletin/SCNG)

A student walks off the Cal State San Bernardino campus on Thursday, Oct 10, 2019. The campus was closed due to heavy winds. (Photo by Will Lester, Inland Valley Daily Bulletin/SCNG)

San Bernardino County firefighters work to put out a blaze in the 9300 block of Palm Lane in the county portion near Fontana on Thursday, Oct 10, 2019. The fire destroyed at least 2 structures and spread to nearby residents yards, destroying at least 3 vehicles and 2 trailers. Cause of the fire is under investigation. (Photo by Will Lester, Inland Valley Daily Bulletin/SCNG)



San Bernardino County firefighters work to put out a blaze in the 9300 block of Palm Lane in the county portion near Fontana on Thursday, Oct 10, 2019. The fire destroyed at least 2 structures and spread to nearby residents yards, destroying at least 3 vehicles and 2 trailers. Cause of the fire is under investigation. (Photo by Will Lester, Inland Valley Daily Bulletin/SCNG)

San Bernardino County firefighters work to put out a blaze in the 9300 block of Palm Lane in the county portion near Fontana on Thursday, Oct 10, 2019. The fire destroyed at least 2 structures and spread to nearby residents yards, destroying at least 3 vehicles and 2 trailers. Cause of the fire is under investigation. (Photo by Will Lester, Inland Valley Daily Bulletin/SCNG)

San Bernardino County firefighters work to put out a blaze in the 9300 block of Palm Lane in the county portion near Fontana on Thursday, Oct 10, 2019. The fire destroyed at least 2 structures and spread to nearby residents yards, destroying at least 3 vehicles and 2 trailers. Cause of the fire is under investigation. (Photo by Will Lester, Inland Valley Daily Bulletin/SCNG)

Crews work on a leaning power pole on San Bernardino Ave as the wind blows in Colton on Thursday, Oct. 10, 2019. (Photo by Jennifer Cappuccio Maher, Inland Valley Daily Bulletin/SCNG)

Dirt and debris blow across a construction site during a red-flag warning in Jurupa Valley on Thursday, Oct. 10, 2019. (Photo by Jennifer Cappuccio Maher, Inland Valley Daily Bulletin/SCNG)



Dirt and debris blow across the 60 freeway during a red-flag warning in Jurupa Valley on Thursday, Oct. 10, 2019. (Photo by Jennifer Cappuccio Maher, Inland Valley Daily Bulletin/SCNG)

Crews work on a leaning power pole on San Bernardino Ave as the wind blows in Colton on Thursday, Oct. 10, 2019. (Photo by Jennifer Cappuccio Maher, Inland Valley Daily Bulletin/SCNG)

On Thursday afternoon, the South Coast Air Quality Management District issued a windblown dust advisory that was to be in place through Friday afternoon as the air quality reached “very unhealthy” levels in parts of Riverside County.

Other areas that could be impacted by poor air quality due to the airborne dust are parts of northern and central Orange County, the San Bernardino Valley and several other parts of Riverside County including the metropolitan area, Hemet and the Coachella Valley.

The dust advisory recommended that those in areas with poor air quality “Limit your exposure by remaining indoors with windows and doors closed and avoiding vigorous physical activity.”

Cal State San Bernardino closed its campus Thursday, Oct. 10, because of the anticipated electricity shutdown.

According to the SCE website, the company looks at historical data to help predict the likelihood of a wildfire occurring.

“During these events, we may need to proactively shut off power temporarily as a result of elevated weather conditions … that can cause a power line to fall and spark, possibly creating a wildfire.”

An outage will last “as long as the dangerous fire weather conditions exist,” according to SCE.

The utility company cut power to 65 customers in unincorporated Kern County on Wednesday afternoon amid gusty winds though it was restored to all but three of them hours later.

The local outages have arrived as unprecedented outages from PG&E have darkened large portions of Northern California.

Here are the communities in each county currently affected by Thursday’s shut-offs:

Kern

Tehachapi

Unincorporated communities of Bird Springs, Horse Canyon, Loraine, Sand Canyon, Twin Oaks

Los Angeles

Palmdale

Unincorporated communities of Agua Dulce, Acton, Boiling Point, White Heather

Unincorporated communities of Fern Ann Falls, Twin Lakes, Deer Lake Highlands, Chatsworth Lake Manor, Santa Susana Knolls

San Bernardino

Fontana

Rancho Cucamonga

Rialto

San Bernardino

Unincorporated communities of Lytle Creek

Unincorporated communities of Muscoy, Devore, Glen Helen Regional Park

Unincorporated communities of Etiwanda, Grapevine Canyon, San Sevain Flats

Unincorporated communities of Devils Canyon, Serrano Village, Kendall

Ventura

Fillmore

Simi Valley

Unincorporated communities of Santa Susana

See also: Tips on surviving a power outage