SAN DIEGO - Firefighting agencies across San Diego County were on high alert Thursday as the Santa Ana winds driving four major wildfires in Southern California were expected to gain strength, with gusts stronger than 80 mph, and create extreme fire danger.
A red flag wildfire warning from the National Weather Service remained in effect Thursday and was set to expire late Saturday night, while a high wind warning was set to expire at 4 p.m. Friday. The red flag warning signifies a high risk of wildfire because of high winds and low humidity -- forecasters said minimum humidity levels were at 5 percent Thursday -- while the high wind warning indicates sustained wind speeds of 40 miles per hour and 58-mph gusts.
Even stronger gusts were expected throughout Thursday potentially exceeding 80 mph, according to the U.S. Forest Service. Cal Fire officials said the Southern California region is bracing for "epic winds ... and extremely dry conditions."
Hi-resolution forecast wind gusts today. Winds will rapidly increase this morning just after daybreak with potential for damaging winds (60mph+) along the coastal-mountain slopes and east #SD Cnty. #CAwx pic.twitter.com/AyCb01bdtF
— NWS San Diego (@NWSSanDiego) December 7, 2017
"The fire potential with this Santa Ana event is extreme," the Forest Service said on its Santa Ana Wildfire Threat Index page. "Easterly winds of 20 to 45 mph can be expected with gusts exceeding 80 mph over the higher terrain and in the more wind prone areas. Humidity will be in the 5- to 15- percent range. Fires will spread very rapidly through all fuel types. Any new fires will have a high probability of becoming large in a short period of time."
The conditions expected throughout San Diego County were even more extreme than the dry, windy conditions that fanned the three wildfires that have burned more than 20,000 acres in the Los Angeles area, as well as the 90,000-acre Thomas Fire in Ventura County.
In preparation for the critical conditions, San Diego Gas & Electric cut power at seven locations throughout the eastern portion of the county on Wednesday night leaving roughly 1,350 customers without power.
"An extreme weather event with high winds and dry conditions is underway in select areas of the region," SDG&E officials said. "To maintain public safety, SDG&E has begun turning off power to customers in several communities. Current conditions indicate that power may remain out for several days before it can be safely restored."
The outages were in communities near Valley Center, Santa Ysabel, Julian, Pine Hills, Descanso, Live Oak Springs and Boulevard.
The San Diego Fire-Rescue Department, Cal Fire and other local agencies have also beefed up staffing this week to handle potential fires.
"Meteorologists at the National Weather Service have not seen models for a Santa Ana event like this in many years," San Diego Fire Chief Brian Fennessy said over the weekend. "We are being vigilant in up-staffing to protect San Diegans and their property. We ask that residents practice their evacuation plans and be prepared in case of a wildfire."
Locally, the most critical fire conditions started Wednesday night and continued Thursday morning, with wind gusts expected to peak around 9 a.m. Thursday, forecasters said.
On the upside, mild temperatures are expected to help mitigate the fire danger somewhat, though a warming trend began Wednesday and significant risk will remain due to the strong winds and near-negligible humidity levels, the NWS advised. High temperatures Thursday in San Diego County will be 75 to 80 degrees at the beaches, inland and in the western valleys, 64 to 69 near the foothills and 52 to 61 in the mountains.
But several years of drought coupled with heavy rains last winter have led to significant fire fuel in the form of underbrush and grass, and a lack of recent rainfall coupled with frequent low humidity have dried out that extra fuel, making it ready to burn freely, according to firefighting officials.
The Santa Ana Wildfire Threat Index, which categorizes Santa Ana winds based on anticipated fire potential as extreme, high, moderate, marginal or no rating, predicted that the danger would be extreme Thursday, marginal on Friday and moderate on Saturday and Sunday.
Public safety officials and the weather service cautioned the public to "avoid activities that could spark a fire" and warned of the risks associated with high winds, including power outages and damaged or toppled trees or power lines.