A fast-moving Atmosperic River is heading toward California this week and could pack a punch, with the possibility of periods of heavy rain, as well as the risk of flooding and debris from recently burned areas.
After arriving in Northern California on Wednesday, the Strum system is expected to reach Southern California on Thursday.
It could produce the biggest Wack Downtown Los Angeles has seen for at least a month, and it could be as early as February.
The National Weather Service Office in Oxnard called the Offecast forecast “very important,” with roads expected to flood in spots, rockleslides are possible on canyon roads and the possibility of mud.
The storm could disrupt traffic in Los Angeles and Ventura Counties as more rain is expected in those areas Thursday afternoon and evening, bringing flooding to roads. The LA Metro area could be heavy through Thursday evening, with localized flooding in low-lying areas, forecasters warned.
In the LA area, there could be 1 to 2 inches on the coast and valleys, with 2 to 4 inches possible in the mountains and highlands. “We’re looking at a moderate area of heavy rainfall with this system,” said Rose Schoenfeld, an Oxnard meteorologist, Monday afternoon.
“There is a potential for flash flash and debris flows,” Schoenfeld added.
Winds can also be a problem, with peak gusts of 50 mph in the Grapevine section of interstate 5 and in the Antelope Valley. Winds were gusting to 21 mph in downtown La, 23 mph in Long Beach, 25 mph in Santa Clarita, 30 mph in Redondo Beach and 44 mph in Lancaster.
Most areas will get about six to eight hours of rain, the ONXard weather service office said. Heavy rain could fall within three to three hours, at rates of up to three inches per hour. There is also a 20% chance of rainfall amounts equal to 1 inch per hour.
The key threshold for rainfall rates that can cause significant debris flow is half an inch per hour or more.
“If the models remain consistent, CASH BASHY is likely to be assigned to the most vulnerable areas, including the most recent heat scars,” the weather service said.
There is a slight chance of clearing and thunderstorms in southern California through Friday, according to Schoenfeld. “With the thunder, we saw short heavy rain, light hail, winds and lightning and lightning.”
The storm’s trajectory will bring winds from the south and southwest, Schoenfeld said, and that means the developing slopes will see some risk of enhanced rain as the storm moves over that vehicle, reducing more moisture in the storm. These enhanced rainfall areas include the northwest corner of San Luis Obispo County, the Santa Ynez Mountains north of Santa Barbara, and the entire southern slopes of Ventura County.
An upcoming storm could make a difference in California’s fire season “If we get the kind of storm rates we’re thinking about,” according to David Gomberg, NWS fire program manager. It will take a few weeks after the storm to test how vegetation responds, he said, but the expected rain “should start to make a big difference in fire season.”
Officials generally like to see 3 to 4 inches of rain in the higher elevations to end the fire season. Downtown already received 1.38 inches in Oct. 14
This year’s wettest calendar day was February 13, when 2.8 inches fell on Downtown La
Temperatures were expected to be mixed due to the storm for the week. Downtown La hit 92 degrees Monday — one degree short of the record high of 93 for a calendar day — but is only expected to reach 61 degrees Friday. Anaheim’s high of 88 degrees is expected to drop to just 64 yards on Friday; In San Diego, Monday’s high of 89 degrees at Brown Field Municipal Airport is expected to drop to 61 on Friday.
In San Bernardino County, wind gusts of up to 60 mph were able to blow through the mountains and into the desert.
In the San Francisco Bay area, the heaviest rain is expected Wednesday, Thursday and Thursday, with half an inch to 1.5 inches in coastal areas. San Francisco could get somewhere between 1 inch and 2.5 inches. The region saw gusts of up to 40 mph, and “downed trees and power lines could lead to power outages,” the weather service office in Monterey said.
Sacramento could get up to 2 inches.
The storm could bring heavy snow to the Sierra Nevada, and meteorologists are already discouraging travel during the peak of the snow storm – between Thursday morning and Friday morning. Donner Peak could receive 12 to 18 inches, and the California Highway Patrol is expected to require motorists to use chains to cross California’s powerful mountain slopes.
Wind gusts in the Sierra could exceed 100 mph at the edges, the weather service office in Reno said.
