After an atmospheric river brought mudslides, debris flows, toppled trees and flooding to Southern California over the weekend, another colder storm began hitting the region on Monday. Weather officials in response issued flood and snow advisories for parts of the region urging people to stay safe.
Besides the advisories, a flash flood warning was in place for parts of northern LA County until 9 p.m. Monday including Pasadena, Altadena, Pacoima, Sun Valley, Monrovia and Azusa.
A “pretty notable” atmospheric river landed over the region this weekend, along with some damage, bringing one to six inches of rain across Southern California, according to meteorologists with the National Weather Service.
“For November standards, it’s not too common for us to get an atmospheric river of the potency that we got. Usually, it’s more common that we would receive an atmospheric river that would give us a few inches of rain anywhere between December and March,” said NWS Meteorologist Sebastian Westerink.
Usually Southern California receives about an inch of rain by this point in the year. Rain levels are currently above average, according to Westerink. The amount of rain SoCal has received at this point in the fall ranges from over an inch up to five inches of rain.
Flood advisories issued Monday were due to expire at 9 p.m. They were for areas including Malibu, Woodland Hills and Santa Monica. Many areas saw only light rain, but enough to dampen streets heading into the afternoon commute.
Forecasters said the rain would continue to fall into late Monday night, “with decreasing showers continuing into Tuesday.”
“Behind the front (Monday night) and Tuesday, an unstable and showery pattern will prevail as the upper low drops southward,” according to the NWS. “By Tuesday evening, rainfall totals with this system are expected to range from half an inch to one inch for coastal/valley areas with one to two inches for the foothills and mountains.
Rainfall rates through Tuesday are expected to generally be under half an inch per hour and will generate nuisance flooding across the area. But forecasters warned that isolated pockets could see rain rates of about an inch per hour, which could trigger more serious flooding and debris flows. A dusting of snow was also possible along the Grapevine stretch of Interstate 5 on Tuesday morning.
“Along with the rain and snow, thunderstorms will be a risk … through Tuesday. As the upper low drops southward today, a cold and unstable air mass will bring a threat of thunderstorms to all areas. On Tuesday, the threat of thunderstorms looks to be confined to LA county as well as interior sections of Ventura and Santa Barbara counties,” the NWS said.
The storm system was expected to be out of the area by late Tuesday, with the area getting a respite from the rain on Wednesday. But another storm system was expected to arrive in the Los Angeles area by Thursday afternoon.
Forecasters said that system could drop another quarter- to three-quarters of an inch of rain.
The National Weather Service also issued a Winter Weather advisory on Monday afternoon for the San Gabriel and San Bernardino Mountains that will be in effect until 10 p.m. on Tuesday. Two to five inches of snow is expected to fall at elevations above 6,000 feet. Areas around 5,500 feet elevation could also see some powder. The affected towns include Running Springs, Big Bear and Wrightwood. Drivers were advised to proceed with caution.