LOS ANGELES (CNS) — At the peak of a Southland heat wave, the National Weather Service today issued a red flag warning effective through Thursday for the San Gabriel Mountains in Los Angeles and Ventura counties and the foothills in the Antelope Valley, citing high heat, low humidity, dry conditions and the expectation of high winds.
The warning, which denotes a heightened risk of wildfire, took effect at noon on Monday, Aug. 15,  and remain in force through 9 p.m. Thursday, Aug. 18. It is the first red flag warning issued since the region’s heat wave began Aug. 13. Even though the heat wave has been projected to end Wednesday, Aug. 17, forecasters said an “elevated fire danger” will exist in inland areas through Thursday because a hot and dry air mass is parked overhead, and an onshore flow will generate gusty winds.
According to the NWS, the hot air will remain in place through mid-week, its presence coinciding with the strengthening flow. The coast will cool down, but “all interior sections of Southern California will continue to see elevated fire danger,”  forecasters said.
The most critical fire weather conditions will occur across the mountains of Los Angeles and Ventura counties and the foothills in the Antelope Valley — areas where the presence of “extremely dry fuels” contributes to “critical red flag conditions,” according to the NWS.
Onshore winds will churn up strong gusts in the mountains, and even stronger gusts in the Antelope Valley through Thursday evening, according to the weather service. At the same time, single-digit humidity levels will prevail, dipping to as low as 3 percent, with little improvement even at night, it said.
NWS forecasters said stiff winds are expected in the Antelope Valley — between 20 and 30 mph, gusting to 45 mph, weakening at night, when it will blow at between 10 and 20 mph, with gusts of 25 mph.
The heat wave is the result of an upper-level high-pressure system combined with weakening onshore flow, the NWS said. Temperatures in Los Angeles and Orange counties will rise today, reaching triple digits across the Antelope, Santa Clarita and San Fernando valleys and the San Gabriel Mountains at lower elevations and the foothills. They will decline a few degrees over the
coming days beginning Tuesday, Aug. 16.
“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.