SAN FRANCISCO – Just three days after a record-breaking storm brought significant rain, widespread flooding and significant mountain snow to much of California, another, perhaps even more powerful double whammy of an atmospheric river and bomb cyclone is targeting the region this week that could become one of the more impactful storms to strike the state in years. Mandatory evacuation orders have even been issued ahead of the storm for neighborhoods with a high risk of flooding.
In this case, the developing storm will tap into abundant tropical moisture available in the Pacific Ocean, creating a reasonably strong “atmospheric river” that will carry copious amounts of moisture from Hawaii to California.
“Basically, an (atmospheric river) is a river in the sky of water vapor, and when it hits the mountains, (the moisture) is forced up over the mountains,” Marty Ralph, Director of the Center for Western Weather and Water Extremes, told FOX Weather. “That upward motion causes clouds and precipitation to form, and the faster the flow of air and water vapor is hitting the mountains, the faster the rain is falling, so you get more and more rain with the stronger ARs hitting the mountains.”
This specific type of atmospheric river, known as the “Pineapple Express,” in a nod to the storm’s fuel source due to its Hawaiian origins, is set to bring significant moisture to California. Think of this as a narrow pipeline of moisture that originates in the tropics.
Flood Watches span much of the state, from near the Oregon/California border to just north of the Los Angeles area.
Some areas along the northern and central California coast could see 5-8 inches of rain, while farther inland, rainfall totals in the mountains and their foothills could approach 8-12 inches in some spots.
The San Francisco area, which saw its second-wettest day on New Year’s Eve, could see an additional 2-5 inches of rain with locally higher amounts. Even the Los Angeles area could have 1-3 inches of rain – with up to 6 inches possible in the Southern California mountains – by the time the storm system moves through.
“A lot of the focus was on the Sacramento Valley, the Bay Area and the San Joaquin Valley, but LA, get ready,” said FOX Weather meteorologist Britta Merwin. “We got rain on the way, and it’s going to be moving in as we go into Thursday morning.”
Since atmospheric rivers have been dropping near record amounts of rain and snow across California since before the Christmas holiday, forecasters worry additional heavy rain could lead to more flooding and landslides.
‘Likely loss of human life’ from atmospheric river impacts
Meanwhile, the bomb cyclone will create a tremendous difference in pressure across regions, leading to widespread strong wind events that could last for several hours.
High Wind Watches span much of the state into Thursday morning for gusts to 50 mph in the San Francisco Bay Area, 55 mph gusts in the Sacramento Valley and 65-70 mph gusts possible along the coastal and mountainous regions.
With heavily saturated grounds and hours of such wind speeds, several falling trees and power outages are likely. There could also be potential damage from flooding and mudslides.
National Weather Service forecasters in San Francisco were not mincing words about the upcoming threat.
“To put it simply, this will likely be one of the most impactful systems on a widespread scale that this meteorologist has seen in a long while,” an NWS meteorologist in San Francisco wrote in their forecast discussion Monday evening. “The impacts will include widespread flooding, roads washing out, hillside collapsing, trees down (potentially full groves), widespread power outages, immediate disruption to commerce, and the worst of all, likely loss of human life. This is truly a brutal system that we are looking at and needs to be taken seriously.”
While rain will fall at the lower elevations across the West, as you get higher in elevation, snow is expected. Some of the highest peaks of the Sierra Nevada could see an additional 2-3 feet of snow by Friday when the storm systems move through.
There is no (sun)light at the end of the tunnel yet
This latest storm will eventually push through by late Thursday or Friday, but there is scant hope for drier weather in the Golden State anytime soon.
Another robust storm system is eyeing the state for the weekend, and extended forecasts suggest additional rain is likely on multiple days next week, adding another several inches of precipitation to the state.
Despite relentless atmospheric rivers, drought still factor in California
Several inches of rain in the forecast on top of what’s already fallen this winter is surely appreciated in a region mired in a years long drought. While every drop helps, the area has a long way to go.
“At this point in time, we still have another four or five months in our snow season and in our typical rainy season,” Andrew Schwartz, lead scientist at the Central Sierra Snow Lab, said last week. “That means that while we’re kind of scoring the touchdown in the first quarter of the game. Right now, we still have three-quarters left, and there’s a lot that can happen.”
Schwartz said last year’s winter season started well with a record-breaking December mountain snowfall.
“But January through March kind of shut off, and we didn’t see as much precipitation come through in that period as we would have wanted,” he s
Even an average snowfall season wouldn’t be enough to get the region out of drought.
“At this point in time, we realistically need about an extra winter’s worth of precipitation,” Schwartz said. “So, it’s not going to happen in one year. At minimum, we’re probably looking at three to four of above-average before we can really talk about getting out of the drought.”
In an average season, the lab sees 30 feet of snow. An extra season’s worth of snow would mean 60 feet in one year. He said it is a “high task to try to take on.”