Record-breaking rain lashes California, with more on the way
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A record-setting atmospheric river has moved out of California, but the stage is set for even more rain in the week ahead.
Following a relatively modest-looking storm that’s expected to arrive in Southern California on Thursday afternoon, forecasters are tracking another, potentially more powerful system that could douse the Southland before or around Valentine’s Day.
There is now a 20% chance that there could be high amounts of rain between Feb. 12 and Feb. 15, according to Ryan Kittell, a meteorologist with the National Weather Service’s Oxnard office. That’s up from a 10% chance that was forecast a day earlier.
Back-to-back atmospheric river storms are set to hit Los Angeles County this week — giving the region much-needed moisture ahead of another potential round of Santa Ana winds.
“It’s not a slam dunk that Southern California is going to be wet, but the odds are much more favorable — increasing especially the past day or so — that we will have a significant atmospheric river in California, and that significant rainfall could make it into Southern California,” said Alex Tardy, a meteorologist with the National Weather Service’s San Diego office.
High amounts of rain would mean 2 to 4 inches or more on the coast and in the valleys, and 4 to 8 inches or more in the mountains and foothills of Los Angeles, Ventura, Santa Barbara and San Luis Obispo counties.
The forecast remains murky, though. There’s a 50% chance of moderate amounts of rain. There is also a chance of low rain or no rain at all.
If it does arrive, the storm would probably be an atmospheric river.
Atmospheric river storms are long plumes of water vapor that can pour over from the Pacific Ocean into California. They carry so much water that they’re said to be like a river in the sky. Just a few atmospheric river events can bring California from one-third to one-half of its annual precipitation.
“The message is that there is a growing potential for higher totals and higher impacts,” Kittell said. A super-soaker storm is “still not the most likely outcome, but enough to really keep an eye on.”
Although this week’s atmospheric river storm was weak by the time it arrived in Southern California and brought few disruptions, it packed a wallop farther north — breaking daily rainfall records in San Francisco, San Mateo County and Sonoma County, causing flooding of the Russian River in Guerneville, and near Hopland, in Mendocino County. A house in Forestville slid into the Russian River after a rain-saturated hillside gave way, and floodwaters temporarily closed lanes of U.S. 101, Interstate 5 and California 99 across the region.
Whether next week’s storm could have a similar effect in Southern California is unclear. The duration is hazy. It might bring steady rain that lasts six to 12 hours, or it could last as long as one to two days, Kittell said. And it’s still too early to tell how intense the rain might be — a key factor in determining the threat of debris flows and mudslides in recent burn areas. Meteorologists say the risk of significant debris and mud flows starts when rain falls at a rate of half an inch per hour.
California’s snowpack stands at 65% of average for this time of year. After a dry January, major storms are forecast to bring more rain and snow.
“We’re not quite confident that we will get the brunt of it here in SoCal. We might just get portions of it,” Tardy said, “but it could be a wetter storm than what we’re seeing Thursday night and Friday of this week.”
That storm — expected to be delivered by a weak atmospheric river — is set to peak between noon Thursday and 6 a.m. Friday.
On-and-off light rain could come earlier Thursday, especially in the foothills of Los Angeles and Ventura counties.
Forecasters say ‘Pineapple Express’ storm will probably be beneficial for Los Angeles and Ventura counties, helping to reduce the risk of wildfires.
“The overall message is — still — this is going to be a beneficial rain, just like the rain we just saw [Tuesday] night, with generally minor impacts and threats or risks,” Kittell said of Thursday’s storm.
Over a two-day period ending at 2 p.m. Tuesday, Long Beach saw 0.12 of an inch of rain; downtown Los Angeles, 0.24 of an inch; Los Angeles International Airport, 0.34 of an inch; Canoga Park, 0.39 of an inch; Thousand Oaks, 0.44 of an inch; Fillmore, 0.72 of an inch; and Santa Barbara, 1.2 inches.
During this week’s second storm, Redondo Beach, Long Beach and Thousand Oaks could get about half an inch of rain; Santa Clarita and Canoga Park, three-fifths of an inch; downtown L.A., Covina and Oxnard, about three-quarters of an inch; and Santa Barbara, 1.24 inches.
There’s a 5% chance of thunderstorms. Rainfall rates are expected to be between one-tenth of an inch per hour and a quarter of an inch per hour, though there could be stronger isolated periods of rainfall.
“This is the type of storm that we really want in general — light, steady rain, not all coming down at once,” Kittell said. Minor road flooding and falling rocks on canyon roads are possible.
There’s a very low risk — less than 5% — of rain falling so hard that debris flow and mudslides would be triggered in recent burn areas, according to Kittell. If significant debris flow does happen, it would be the result of a stray intense storm cell materializing directly over a burn scar.
Los Angeles and Ventura counties could see wind gusts from the southeast and southwest, peaking between 6 p.m. Thursday and Friday at 8 a.m. Gusts could reach 30 mph to 40 mph in San Luis Obispo County, northern Santa Barbara County and L.A. County’s high desert, but are expected to be milder in the Los Angeles metro area and most of Ventura County, with gusts around 10 mph.
At LAX, winds could come out of the east, Kittell said. They won’t be particularly strong, but they may be strong enough to change flight operations, prompting delays.
Friday night and the weekend are expected to be dry in Southern California, Kittell said, with periodic wind gusts.
The fire weather risk will be minimal, given recent rains.
“This is not a true Santa Ana. It’s more of a northerly type wind event, and it’s dry, but not terribly dry,” Kittell said. “The recent rains are sufficient enough to dampen [and] limit any fire weather concerns, at least for this next push.”
From Friday night through Monday, gusts could reach 12 mph in Covina; 14 mph in downtown Los Angeles and Long Beach; 21 mph in Canoga Park, Thousand Oaks and Fillmore; 22 mph in Oxnard; 26 mph in Santa Clarita; 28 mph in Acton; 41 mph in Lancaster and 58 mph at Pyramid Lake.
Although the recent moisture will help reduce wildfire risk across Los Angeles and Ventura counties, it probably won’t be enough to definitively end fire season given the region’s severe winter rainfall deficit.
“If we get a long dry period — for a week or two or three — following the rain [this week], then we might be back into that fire weather danger,” Kittell said, especially if Santa Ana winds return. Severe Santa Ana winds are most common between October and March, though they can occur as late as May.
Downtown L.A. has received just 0.7 of an inch of rain since the water year began Oct. 1; the average for this time of year — a little more than four months into the water year — is 7.68 inches. The annual average is 14.25 inches.
Downtown’s driest water year on record ended Sept. 30, 2007, when only 3.73 inches of rain fell. The following summer and fall were a bad fire season — with the largest blazes being the Zaca fire that burned more than 240,000 acres in Santa Barbara County and the Witch fire in San Diego County, which burned nearly 198,000 acres, destroyed 1,650 structures and killed two people.
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