Major SoCal Storm To Drench Region, Trigger Flash Flooding And Tornados

The first substantial storm of the season is expected to douse the Southland this week, bringing showers, gusty winds and significantly cooler temperatures, weather officials said.

Though the storm is forecast to be brief, a flood watch will take effect in many cities, particularly where burn scares from past wildfires could pose a threat.

"An early season storm system in the Pacific Northwest will dig south into the region through Tuesday," the National Weather Service said Monday morning. "Periods of rain and high elevation snow, heavy at times, will develop from north to south from this afternoon through Tuesday."

The low-pressure system is expected to move southward on Monday, triggering strong onshore winds Monday into Tuesday night, followed by rain from the coast to the mountains, forecasters said.

"Cooler temperatures with drier conditions will linger into Thursday, then a warming trend will develop for the end of the week," NWS forecasters wrote in a Monday forecast discussion.

By late Monday, strong wind gusts are expected to develop across the mountains and deserts, reaching 30 to 40 mph and exceeding 55 mph in wind-prone passes and slopes. Forecasters warned that the system will also draw in colder air, bringing the possibility of high-elevation snow and rainfall rates that could exceed a quarter-inch per hour in some areas.

READ MORE: Burn-Scarred Malibu Urged To Prepare For Mudslides, Flash Flooding

In Los Angeles County, the storm could bring between three-quarters of an inch to 1.5 inches of rain, along with a chance of thunderstorms, hail and even waterspouts or a weak tornado near the coast, according to the weather service.

A flood watch has been issued from Monday through Tuesday evening for recent burn areas in Los Angeles, Ventura, Santa Barbara and San Luis Obispo counties.

Officials in Pasadena urged residents to prepare for possible flooding, particularly in the Eaton Fire burn area in Altadena. K-rails, or temporary concrete barriers, have been installed to help protect vulnerable neighborhoods from mud and debris flows, according to the city. Residents can also pick up sandbags from Los Angeles Fire Department stations 37 and 38 and sign up for emergency alerts via NotifyLA at emergency.lacity.gov.

Further south, rainfall is expected to begin Monday night and continue through Tuesday night across Riverside and San Diego counties.

The heaviest rainfall is expected Tuesday, when temperatures will dip as much as 10 to 20 degrees below normal in inland valleys, mountains and deserts. Downtown San Diego is forecast to reach only 68 degrees, the weather service said.

By Wednesday, the storm system will move out of the region, giving way to gradual warming.

"For next weekend, the warming continues inland while marine layer clouds and fog return to the coastal areas," the NWS predicted.

See the forecast across SoCal on Tuesday, according to the NWS:

Los Angeles: High near 64. South southeast wind 10 to 15 mph becoming southwest in the morning. Chance of precipitation is 100%. New rainfall amounts between three quarters and one inch possible.

Malibu: High near 64. Southwest wind 10 to 15 mph, with gusts as high as 20 mph. Chance of precipitation is 100%. New rainfall amounts between a half and three quarters of an inch possible.

Newport Beach: High near 67. South wind 10 to 20 mph, with gusts as high as 30 mph. Chance of precipitation is 90%. New rainfall amounts between a quarter and half of an inch possible.

Mission Viejo: High near 64. South wind 10 to 15 mph, with gusts as high as 25 mph. Chance of precipitation is 90%. New rainfall amounts between a half and three quarters of an inch possible.

Banning: Southwest wind 15 to 20 mph decreasing to 10 to 15 mph in the afternoon. Winds could gust as high as 35 mph. Chance of precipitation is 80%. New precipitation amounts between a half and three quarters of an inch possible.

Palm Desert: A chance of showers, mainly after 11am. Partly sunny, with a high near 76. Northwest wind 5 to 10 mph becoming south in the morning. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

San Diego: Showers likely, mainly after 11am. Mostly cloudy, with a high near 68. South wind 10 to 20 mph, with gusts as high as 30 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

Santee: Showers likely, mainly after 11am. Mostly cloudy, with a high near 67. South wind 10 to 15 mph, with gusts as high as 25 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.