2nd bomb cyclone, atmospheric river in three days to blast US West Coast
Yet another bomb cyclone and atmospheric river are taking aim at portions of the Pacific Coast states to end this week ahead of a third weekend storm that will bring rain to California.
Multiple feet of snow accumulated in the mountains of the Pacific Northwest as intense winds blew down trees at lower elevations from Nov. 19-20.
Two bomb cyclones and atmospheric rivers in one week? It may seem hard to believe, but Mother Nature has the gloves off and will continue to hurl potent storms with gusty winds, big rain and high country snow toward the Pacific Coast states through this weekend, AccuWeather meteorologists warn.
The next bomb cyclone lasting into Friday will not be as intense as Tuesday's powerhouse storm. The powerful storm will make more of a glancing blow from south to north just off the coasts of Northern California, Oregon and Washington, but it will still be close enough and strong enough to bring impacts from wind, rain and snow.
This image was captured on Wednesday, Nov. 20, 2024, and shows the Pacific (left) and the western United States (right). A swirl of clouds over the Pacific was indicative of a bomb cyclone and its eye that was gradually losing wind intensity. A new storm will form and become a bomb cyclone later this week. (AccuWeather Enhanced RealVue™ Satellite).
A bomb cyclone is a storm that strengthens so fast that the central atmospheric pressure plunges 0.71 of an inch (24 millibars) or more in 24 hours or less. The central pressure in Tuesday's bomb cyclone fell a whopping 1.71 inches (58 mb), or more than double the intensity criteria. The "bombing out," or rapid intensification, is important because the faster that the pressure drops in a storm, the faster that new air must rush in to take the missing air's place. This movement of air is the wind.
A bomb cyclone hit Bellevue, Washington, on Nov. 19, 2024, causing high winds, downed trees and power outages in western Washington and Canada. Two people died in the storm.
Strong winds from Tuesday night's intense storm knocked down a tree that killed one woman and cut the power to 600,000 utility customers in western Washington alone.
"The track of the new bomb cyclone will be such as to direct the strongest winds right along the coasts of Washington and northern Oregon, rather than throughout the Interstate 5 corridor and Cascades," AccuWeather Senior Meteorologist Dave Houk said.
By far, the greatest impact from the new bomb cyclone and a more southward-tracking storm that follows will be its precipitation.
Just like the first bomb cyclone, an atmospheric river will develop. This long firehose of moisture from the ocean will be directed at the same areas as the first storm this week, Houk said.
"Once again, the heaviest rain will be directed at areas from Northern California to southwestern Oregon," Houk said, "The timing on the heaviest rain will be into Friday morning. While there will be a bit of a lull, it may not completely stop raining in between the first storm and the next."
Thunderstorms packing hail and gusty winds can occur in some areas between both major storms.
The cumulative rainfall from both storms this week, from Northern California to southwestern Oregon, will generally range from 8 to 12 inches, with an AccuWeather Local StormMax™ rainfall of 20 inches. From 1 to 4 inches of rain will be common along the I-5 corridor and the immediate coasts from Washington to northern Oregon.
The rounds of intense rain produced by back-to-back atmospheric rivers will lead to a high risk of dangerous flash flooding, mudslides, landslides, washouts and erosion.
Farther south, around San Francisco and Sacramento, California, the heaviest rain from the storm will tend to fall to the north, while rainfall will taper off from north to south, beginning over the metro areas. From 12 to 18 inches of rain is forecast to fall around Santa Rosa through Friday morning, while San Jose may receive close to an inch.
"Both the San Francisco and Sacramento areas can expect slow commutes on Friday," Houk said. "Enough rain can fall to lead to flooding in poor drainage areas."
Snow levels for the second storm will be higher than the first, leading to extra melting and runoff at intermediate elevations. Most of the snow will fall above the passes for the late-week storm, but up in the high country, cumulative snowfall this week will range from 1 to 3 feet, with locally higher amounts in the Cascades, Siskiyous and northern Sierra Nevada.
"The tail end of the second storm may attempt to bring spotty showers to Southern California on Saturday," Houk said.
A short time after the second bomb cyclone lifts northward and loses wind intensity off the Washington coast, a third storm will roll in from the Pacific later this weekend.
It is that third storm that will direct rain at a large part of coastal California, AccuWeather Senior Meteorologist Heather Zehr said.
"There is the potential for up to 0.50 of an inch to fall on the Los Angeles area, beginning Sunday morning or midday and continuing into Sunday night," Zehr said, "This will be the first rainfall since May 13, when 0.13 of an inch fell on downtown Los Angeles."
Rain may be more limited around San Diego. Likewise, rain may struggle to travel over the Coast Ranges to the deserts.
"The combination of the second bomb cyclone and the storm later this weekend will bring snow to much of the Sierra Nevada," Houk said. "However, most of the snow that falls will be above that of Donner Pass, California. The ski resorts should be treated well with a thick blanket of snow."
The news is not so good for Thanksgiving travelers over a large part of the Pacific Coast states as well as a large part of the West with more storms forecast to roll in with multiple rounds of rain and mountain snow.
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