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Spokane, Washington  Est. May 19, 1883

Punishing California storm pattern still has a final act

The skyline of downtown Los Angeles is shrouded by clouds on Monday.  (Michael Robinson Chávez/FTWP)
By Matthew Cappucci Washington Post

The weather pattern that brought record-setting rains, fierce winds and prolific mountain snows to California has not completely moved out, even after a three-day onslaught that featured hundreds of mudslides and at one point cut power to nearly 1 million customers. One more wave is coming through, and it will feature a quick burst of precipitation that could trigger flooding in a few more areas.

This final wave, to progress from north to south into Thursday, has prompted continued flood watches around Anaheim and San Diego, while winter weather advisories and winter storm warnings remain in effect for the mountains.

At the same time, the blockbuster storm that hit California between Sunday and Tuesday is spreading downpours to the Arizona desert and snow throughout the Intermountain West. Winter weather alerts stretch from the high terrain of Arizona to Montana.

While the powerhouse storm and atmospheric river responsible for the torrents in California have moved off to the east, weather models show a trailing disturbance that will bring one final burst of precipitation. It’s already working through Northern California and will reach Los Angeles shortly before midnight Thursday. Any given location will see about six hours of precipitation.

In the highest peaks of the Sierra Nevada, an additional 5 to 9 inches of snow can’t be ruled out. For the lowlands, the Central Valley and most of the California coast, another quarter- to half-inch of rain is likely. But south of Los Angeles, amounts could climb over half an inch, with up to 1 to 2.5 inches in the mountains (below snow levels). A thunderstorm or two could sneak into the mix, enhancing rainfall rates.

“This additional rain falling onto saturated soil will increase the flood potential,” the National Weather Service in Los Angeles wrote, “especially if training of cells with high intensity rainfall occurs.”

Between Sunday and Tuesday, the storms unloaded more than a foot of rain in parts of Los Angeles County, which is an exceptional amount.

A rain gauge at the University of California at Los Angeles logged 12.46 inches in 24 hours, which would surpass the 11.5-inch threshold needed to qualify as a 1,000-year rain event, or an episode with a 0.1% chance of happening in any given year. The extreme statistic hasn’t been verified yet, though the rain gauge is operated independently by UCLA and not an “official” observation state. The Weather Service office in Los Angeles is working with the university to investigate the reliability of the sensor.

The official storm total in downtown Los Angeles was 8.51 inches, adding to an already rainy start to its water year, which spans Oct. 1 to Sept. 30. The 15.43 inches since Oct. 1 is 7.63 inches above the normal. “It is also already 118 percent of the normal seasonal rainfall of 14.25 inches,” the Weather Service wrote in a statement.

Los Angeles has received 10.20 inches in February alone, seventh-most on record just six days into the month, with more rain to come.

Its rainfall so far in 2024, 12.25 inches, has surpassed New Orleans, Houston and San Antonio, and more than doubled New York’s total. Miami, known for its tropical climate and frequent rains, has seen just 1.75 inches during this period.

San Diego also received substantial rain – 2.22 inches from this past storm. Since Oct. 1, it has posted 8.27 inches, more than 150% the norm.

The storm that hit California has weakened and become more disorganized while heading east. Still, it has had significant effects, particularly in the Southwest.

Flagstaff, Arizona, had received 16.5 inches of snow through Wednesday morning, its biggest storm of the winter, erasing a snowfall deficit. The aptly named Arizona Snowbowl just to the north of Flagstaff had registered 26 inches as of 7 a.m. local time.

Interstate 40 westbound in Arizona was closed Wednesday morning from mile marker 10 to mile marker 26. No detour was available, meaning drivers would have to plan to use Interstate 10, nearly 200 miles to the south.

In the lower elevations of the Southwest, rain had fallen. The amounts weren’t particularly high but were significant locally given the desert climate. Phoenix got 0.34 inches, and Las Vegas recorded 0.59 inches. That was enough to cause localized flooding.

In Arizona, winter storm warnings have been extended through Thursday, with additional snow showers expected to drop 4 to 6 more inches in spots. Utah’s Wasatch Mountains are expected to see 8 to 16 inches, primarily south of Interstate 80. In the mountains of Colorado, a general 8 to 20 inches of snow, depending on elevation, is expected, with 2 to 3 feet atop peaks above 10,000 feet.

Dramatic improvement will arrive in the West by Friday.