Amid wildfires, Los Angeles’ winter rains to finally arrive. But dry weather could soon return

With red flag fire weather warnings finally set to end Friday morning, Southern California is set for its first real rains of the winter, which would provide some welcome relief in the region’s seemingly endless firefight.

Yet there is concern that this weekend’s rains could provide only temporary relief. After this weekend, a dry spell could return — raising serious questions about whether dangerous fire weather could return sooner than later. One big problem: the Santa Ana wind season can persist through February and March, and one weekend of modest rainfall would be no match for more weeks of dry winds and weather, should that materialize.

Southern California is in the throes of a historically dry start to winter — one for the record books, shattering records that have been collected since the late 19th century. And the region is rapidly running out of time to catch up on the severe deficit in rainfall before the winter rainy season ends.

“We have not been in this territory before for dryness, not this deep into a winter — ever,” said Alex Tardy, meteorologist with the National Weather Service office in San Diego, which also provides forecasts for Orange County and the Inland Empire. “This has really been extreme for Southern California.”

Southern California has been stuck in a punishing weather pattern since October, where not a single significant storm has passed over the region. In January, the weather pattern worsened — with the storm track blocked from “not just Southern California, but all of the West — from Seattle southward,” Tardy said.

The lack of rain came as seven separate Santa Ana wind events hit Southern California in January alone, Tardy said, a dangerous combination in creating fire weather conditions as the air and vegetation dry out, making brush especially flammable. There have been a total of 15 Santa Ana events since November, Tardy said.

“The Santa Ana winds have really taken their toll on sucking the moisture out of the atmosphere,” Tardy said. “There’s no marine layer, because it’s been blown out the sea. The desert has come to the coast.”

Concern about a dry start to February

After this weekend’s rains, the long-term outlook suggests that for Southern California, “we go back, most likely, into a dry pattern,” Tardy said.

It’s the driest start to the water year, which began Oct. 1, on the record books in places like San Diego, Orange County, the Inland Empire, as well as Los Angeles International Airport, UCLA, Van Nuys, Woodland Hills and Camarillo.

For other spots, it’s the second driest start to the water year, which includes places like downtown Los Angeles, which has received just 0.16 of an inch of rain since Oct. 1. That’s only 2.5% of what downtown L.A. gets on average by this point in the season — 6.38 inches of rain. The annual average rainfall for downtown is 14.25 inches.

First real rain of winter expected

This weekend’s rains are mostly expected to bring a welcome respite in the last couple of weeks of almost unrelenting fire weather. There have been red flag warnings in some part of Southern California for 15 of the last 18 days, which are set to end at 10 a.m. Friday.

This week brought a number of new threatening wildfires to Southern California, including the Hughes fire, which burned more than 10,000 acres since Wednesday around Castaic Lake, just north of Santa Clarita. By late Thursday, the Hughes fire was 36% contained. The 23,400-acre Palisades fire was 75% contained, and the 14,000-acre Eaton fire was 95% contained.

The rains are expected to break a record streak of minimal rainfall for downtown Los Angeles, which has not seen more than one-tenth of an inch of rain on a calendar day since 0.13 of an inch of rain fell on May 5. As of Friday, it has been 264 days since downtown L.A. has received one-tenth of an inch of rain or more. That’s a record for downtown — the previous mark was 253 consecutive days, from Feb. 25, 2008, to Nov. 3, 2008.

At the moment, forecasters anticipate widespread rain this weekend. Between Saturday and Monday, downtown L.A., Long Beach and Santa Clarita could get three-fifths of an inch of rain, while Canoga Park and Fillmore could get more than a half an inch of rain, and Thousand Oaks, two-fifths of an inch of rain.

San Diego, Anaheim, Irvine, San Clemente, Riverside and Lake Elsinore could get between 0.7 to 1 inch of rain. San Bernardino, Ontario, Temecula, Oceanside, Escondido and Mira Mesa could get 1 to 1.5 inches of rain.

(National Weather Service)

But this is a tricky storm system to forecast, said meteorologist Ryan Kittell of the weather service’s Oxnard office, which issues forecasts for Los Angeles, Ventura, Santa Barbara and San Luis Obispo counties. This storm is fueled by a low pressure system that’s coming south, from Canada, and current projections place that low pressure system right over the Southern California coast.

If that low pressure system moves even a little bit to the west, more rain could fall than expected; if it wobbles a little to the east, the storm could result in less rain than expected, Kittell said.

Periods of rain could start as early as Saturday morning and last through Monday night. But the highest chance for rain will be Saturday night into Sunday, Kittell said of Los Angeles, Ventura, Santa Barbara and San Luis Obispo counties.

The heaviest potential for rainfall will be Sunday and Monday for San Diego, Orange, Riverside and San Bernardino counties.

Risk of thunderstorms and landslides

Most likely, the rain that does fall will be of a light intensity, spread out over many hours.

But there is a 10% to 20% chance of thunderstorms across the region, which could happen at any time, and could bring isolated, brief heavy rainfall at rates of half an inch an hour, Kittell said.

That’s a significant number, because that’s the starting threshold for recently burned areas to develop debris flows — a type of damaging landslide that involves water rapidly flowing downhill, picking up mud, rocks, branches and sometimes massive boulders.

There will likely be a couple of spots across the region that do see these thunderstorms, according to Kittell. The question is whether they’ll happen to appear right over recently burned areas.

Putting it all together, that means there is a 5% to 10% chance of damaging debris flows in recently burned areas in Los Angeles and Ventura counties from this weekend’s storm, Kittell said.

There is also a moderate risk of small hail.

Snow levels could fall to an elevation of 3,500 to 4,500 feet above sea level. There could be 5 to 10 inches of snow in the San Gabriel Mountains. There’s a potential for perhaps one inch of snow on the Grapevine section of Interstate 5, especially on Sunday, which could result in delays on the freeway, Kittell said.

(National Weather Service)

Wrightwood and Big Bear Lake could get 8 inches to 12 inches of snow. That raises the prospect of authorities requiring motorists to install chains on tires when driving to mountain areas like Big Bear.