SAN DIEGO -- A wildfire warning prompted by strong Santa Ana winds and near-negligible humidity levels kept the San Diego area an high alert Tuesday as destructive, out-of-control wildfires driven by similar conditions tore through parts of Los Angeles and Ventura counties.
Tuesday afternoon, the National Weather Service extended its "red flag" warning -- signifying potentially "extreme" combustion hazards in local coastal, inland-valley and mountain communities -- until 6 p.m. Saturday. The warning initially had been set to expire late Thursday night.
Additionally, the federal agency lengthened an accompanying high-wind warning for the county's valleys and mountains by 24 hours, moving back its scheduled expiration to 4 p.m. Friday.
The most critical fire hazards likely will occur Thursday and Friday, forecasters said.
On the upside, mild temperatures are expected to help mitigate the fire danger somewhat, though significant risk will remain due to the strong winds and humidity levels in the 5- to 15-percent range, the NWS advised.
To prepare for the dicey conditions, both the San Diego Fire-Rescue Department and San Diego Gas & Electric beefed up staffing levels this week. The former agency put several extra strike teams -- equipped with 10 brush rigs, five engines, two water trucks and two helicopters -- on alert, while SDG&E officials staged field crews and contract firefighters in areas where winds are expected to be the strongest.
"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. "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."
SDG&E -- which last week lost a ruling in relation to the 2007 wildfires the company was found responsible for starting -- said it may need to turn off power this week in certain areas "if weather conditions threaten the integrity of our system and create the possibility of an imminent emergency."
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 the extra fuel, making it ready to burn freely, according to firefighting officials.
The U.S. Forest Service 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 on Thursday and high on Friday. Tuesday, the index listed the threat as marginal.
On Thursday, with some local gusts possibly exceeding 80 mph, wildfires potentially will " have extreme growth, will burn very intensely and will be uncontrollable," according to the Forest Service.
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.