An elevated danger of wildfire threatened Southland areas away from the coast Tuesday but a particularly acute risk prevailed in the Antelope Valley and the San Gabriel Mountains in Los Angeles and Ventura counties because of high heat, very low humidity, bone-dry vegetation and onshore winds, forecasters said.
A red flag warning denoting a high risk of wildfire was issued by the National Weather Service Monday for the mountains and foothill areas of the Antelope Valley. The NWS took the unusual step of making it a four-day affair, saying the warning — the first issued since the region’s heat wave began Saturday — would expire only at 9 p.m. Thursday.
The NWS blamed the danger of fire on a hot, dry air mass parked over the region, onshore winds expected to produce powerful gusts, “extremely dry fuels” and humidity levels plummeting to an unusually low 3 percent and not rising much even overnight, remaining below 20 percent.
“While all interior sections of southwest California will continue to see elevated fire danger, the most critical fire weather conditions will occur across the mountains of Los Angeles and Ventura counties as well as the foothills of the Antelope Valley, according to an NWS statement.
The mountains will be swept by southwest winds of between 15 and 25 miles per hour accompanied by gusts of between 30 and 40 mph, mainly in the afternoon and evening, NWS forecasters said, adding that the most severe mountain winds will be on the L.A. County side of the San Gabriels.
Foothill areas of the Antelope Valley are expected to be buffeted by winds of between 20 and 30 mph, gusting to 50 mph, though they will lose strength at night, blowing at between 10 and 20 mph, with 25-mph gusts.
If a fire begins, “conditions are favorable for extreme fire behavior and rapid spread of wildfire, which would threaten life and property,” the NWS statement said.
The heat wave, the result of an upper-level high-pressure system, is expected to begin dissipating Wednesday. In the meantime, it poses a risk to people and animals, officials said.
“The prolonged heat wave will likely result in an increased risk of heat-related illnesses, especially for the homeless, elderly, infants and anyone participating in outdoor activities,” according to the NWS.
Forecasters urged residents to stay well-hydrated, wear light-colored lightweight clothing, stay indoors when temperatures are at their highest and never leave people or pets in parked vehicles in hot weather, even for a short time.
People with heart disease, asthma or other respiratory diseases who live or work in high-heat areas are especially urged to minimize outdoor activities. This will be especially important today in the San Gabriel Valley, where air quality will be unhealthful for sensitive groups, and the San Fernando and Santa Clarita valleys, where air quality will be just plain unhealthful.
Los Angeles city animal services officials, meanwhile, warned pet owners to ensure their cats, dogs and other animals are kept cool and to watch for signs of heatstroke, such as fast and noisy breathing, difficulty swallowing and distressed behavior.
If heatstroke is suspected, pet owners should place a cold, wet towel on the back of the animal’s head, and towel-wrapped cold compresses on their back legs and belly. The pet should be immediately taken to the veterinarian to be checked.
Highs Tuesday will be in the mid 80s in downtown L.A., 98 in Yorba Linda, 102 in Lancaster and 103 in Woodland Hills.