A strong storm system is expected to drench much of Southern California with rain and cover mountaintops with snow beginning late Monday evening and peaking Tuesday, raising fears of flooding and potential debris flows.
National Weather Service forecasters previously dubbed it “the most significant storm of the season.” Coastal areas and the valleys could get up to 3 inches of rain during the storm, while mountains and foothills could see up to 5 inches.
“Due to the threat of heavy rain bands and a slight chance of thunderstorms capable of producing high intensity short duration rainfall, there will be the potential for debris flows over recent burn areas as well as significant roadway flooding,” according to the NWS.
Rain will progress from northwest to southeast, with the heaviest rain over Los Angeles County expected to fall between 7 a.m. and 5 p.m. Tuesday, forecasters said.
“On Tuesday the system will move into L.A. County and will likely make a mess of rush hour traffic. A very strong jet will move over the area,” forecasters said.
The NWS issued a flash flood watch that will be take effect at 3 a.m. Tuesday and remain in place until 6 p.m. Tuesday in recent county burn areas — from the Bobcat, Ranch 2, Dam, Lake and Palisades fires. Forecasters warned that those areas could see intense downpours with an inch or more of rain per hour.
“Residents near these burn scars should prepare for potential flash flooding and debris flow impacts,” according to the NWS.
A flood watch will also be in effect throughout Tuesday in Orange County coastal and inland areas and in the Santa Ana Mountains and foothills.
The storm will also bring strong winds to the area, likely sweeping over and down the San Gabriel range and bringing warning-level gusts to the Antelope Valley late Monday evening.
“Periods of strong south to southwest winds are also expected with this system, especially in the mountains, deserts, and high elevation valleys where damaging wind gusts of 50 to 65 mph will be likely,” according to the NWS. “Remaining coastal and valley areas will see widespread wind gusts of 30 to 50 mph. In addition, localized wind gusts up to 50 mph will be possible anywhere that has thunderstorms or heavier convective showers.”
About 1 to 3 feet of snow will fall on mountains above 7,000 feet, but there could be some snow accumulation in the Grapevine area.
The storm will be accompanied by chilly temperatures, with daytime highs in the 50s Monday and Tuesday and lows dropping into the 30s Tuesday night in the mountains and parts of the San Fernando Valley, and into the 20s in the Antelope Valley.
Health officials advise the public not to swim or surf in ocean waters at and around discharging storm drains, creeks and rivers after significant rainfall due to a possible increase in bacteria, chemicals, debris, trash and other public health hazards.
The Los Angeles Fire Department and county Office of Emergency Management issued a series of reminders related to the potential for mud and debris flow. Among them were:
— Acquire any needed sandbags and instructional materials at your local Los Angeles County fire station.
— Have an emergency plan in place.
— Monitor radio and TV news closely for information about weather conditions and flooding in your area.
— If your neighborhood is evacuated, identify important items to take (e.g., computers, photos, important documents, medications, and other essential items for your family and pets).
— Have enough food and water to supply your family for at least a 72-hour period.
— Remember to include a radio and flashlight with fresh batteries in your emergency kit.
— Stay away from flood control channels, catch basins, canyons, and natural waterways that are vulnerable to flooding during periods of heavy rain.
— Do not attempt to cross flooded areas and never enter moving water on foot or in a vehicle.
“Our emergency response officials are world-class and will stand ready to defend lives, property and infrastructure if there are emergencies caused by this storm,” said Kevin McGowan, director of the county Office of Emergency Management. “But, we need collaboration from the public. It is critical for residents to be aware and prepared so that they can help keep themselves safe.”