SAN DIEGO (CNS) - Dense Santa Ana fog was rolling in along the San Diego County coastline Saturday ahead of the gusty winds, warm weather and low relative humidity that were expected to raise the risk of wildfires starting Monday in the mountains and valleys.
The National Weather Service issued a dense fog advisory, which was set to remain in effect until 9 a.m. Sunday. Fog along the coastline from Pacific Beach to the U.S.-Mexican border was expected to spread a few miles inland this afternoon and north along the coast this evening, according to the NWS.
Forecasters warned that visibility could drop to less than a quarter-mile and drivers on parts of Interstates 5, 8 and 805, along with state Routes 78 and 52 could be impacted. The fog could affect flights into and out of Lindbergh Field in San Diego and McClellan-Palomar Airport in Carlsbad.
While the foggy conditions are expected to improve by mid-morning Sunday, the weather service scheduled a Red Flag Warning to take effect at 3 a.m. Monday and extend until 6 p.m. Wednesday for valley and mountain areas including the Palomar and Descanso ranger districts of the Cleveland National Forest.
"A strong ridge of high pressure aloft and at the surface over the Great Basin will result in Santa Ana conditions over Southern California much of next week," the warning stated. "Very dry air, much above normal temperatures and periods of strong, gusty winds will result in critical fire weather conditions at times Monday through Wednesday."
NWS forecasters said the lack of rainfall this winter had further dried vegetation well beyond what was normal for this time of year in many areas.
East to northeast winds of 20 to 30 mph with gusts of up to 50 mph and isolated gusts of up to 60 mph are likely in wind-prone spots along San Diego County's coastal mountain slopes and foothills, according to the NWS. The winds are expected to begin speeding up Sunday night with strongest winds Monday and Tuesday, but they should weaken Wednesday.
Afternoon highs during the warning period are expected to be in the 80s, forecasters said. The warm and dry weather was expected to further dry fuels through Friday and continue to raise the wildfire risk.
The NWS said relative humidity would fall into the teens Sunday night at higher elevations, which would then spread to the valleys Monday morning.
"A combination of strong winds, low relative humidity, above normal temperatures and very low fuel moisture will contribute to extreme fire behavior," the NWS said.