SAN DIEGO, Calif. – The first of two atmospheric rivers, also known as the “Pineapple Express,” hit the West Coast on Wednesday, bringing heavy rain and mountain snow as residents braced for potentially dangerous conditions.
The “Pineapple Express” is an atmospheric river that builds up in the tropical Pacific Ocean, and when it descends in the western United States, it can bring heavy rain and snow. Satellite images of the first storm on Wednesday showed clouds along the coast from Los Angeles, California, to Juneau, Alaska, according to AccuWeather.
“The first storm will continue to transport copious amounts of moisture like a giant firehose southward across California through Thursday evening,” AccuWeather said.
The “moisture plume” will move along the West Coast and into Southern California overnight Wednesday, and is expected to bring heavy rain across the region and state, according to a National Weather Service forecast.
Snow is also expected on high mountains in parts of northern and central California, according to the weather service.
More than 20 million people across the state were under weather warnings on Wednesday due to increased risks of flooding and high winds. According to AccuWeather, the pair of storms could cause mudslides, power problems, coastal erosion and property damage.
The California Governor's Office of Emergency Services has activated its operations center and deployed personnel and equipment to areas most at risk.
While Californians will see a partly dry weekend, a second storm is expected to hit Sunday into Monday. According to Daniel Swain, a climate scientist at the University of California, Los Angeles, the second storm has the potential to be much stronger.
“Pineapple Express”:Atmospheric rivers aim for California to bring flood risks of up to 4 feet of snow
Heavy rain and scattered thunderstorms in central and southern California
The storm moved towards the Central Coast where warnings were issued about possible flooding for rivers, streams, some roads and areas destroyed by previous wildfires. Meteorologists said the Central Coast could see waves as high as 18 feet on Thursday and Friday.
From central to southern California, the Weather Prediction Center warned of heavy rain falling at a rate of 2 to 4 inches. “Widespread scattered thunderstorms” in some areas may cause scattered rain at rates of up to 1 to 1.5 inches per hour, according to the center.
The storm makes landfall in Northern California
The river-fed weather storm touched down Wednesday in Northern California, bringing brief hourly rainfall of 0.5 to 1 inch, according to the Weather Prediction Center. In Pacifica, a coastal city in San Mateo County, more than an inch of rain was recorded in one hour.
The center said that heavy rains could lead to flash floods during Wednesday night along the northern and central coast of California. The Bay Area Weather Service issued a flood warning for parts of the region, including San Francisco, San Mateo, Marin and Sonoma counties until late Wednesday.
A high wind warning was also issued for counties along the northern and central coast. Peak winds ranged from 60 to 70 mph, the weather service said.
Many parks and other outdoor events or programs across the Bay Area were closed Wednesday due to wet and windy conditions. San Francisco cable car service has been halted as a precaution.
The California Highway Patrol previously warned drivers on Twitter to use “extra” caution on the roads.
“We responded to our first vehicle accident on I-280 in the rain today,” Cal Fire and the Redwood City CHP said Wednesday afternoon. “There were no injuries… Please slow down.”
In Sacramento, the weather service warned of a 10% to 25% chance of thunderstorms as the storm system moves inland. In addition to moderate to heavy rain and gusty winds, thunderstorms may also cause lightning and small hail.
Pacific Gas & Electric (PG&E) reported some power outages Wednesday evening. More than 2,200 people were without power in Redwood City, and nearly 2,500 people were left in the dark in Sacramento, according to PG&E's outage map.
Up to 4 inches of rain is expected in parts of Northern and Southern California
Much of Northern California and coastal areas of Southern California will receive between 1 and 4 inches of rain, according to AccuWeather. Locally, greater amounts up to 6 inches are likely along the “west- and southwest-facing Coast Ranges.”
Strong winds will also affect northern and central California through Thursday, increasing the risk of downed trees, AccuWeather said.
“Given the saturated soil, trees have fallen and will likely lead to power outages,” the report warned. National Weather Service Bay Area On X.
In San Francisco and Sacramento, travel conditions will be at their worst starting Wednesday. Meanwhile, from Los Angeles to San Diego, residents can expect travel delays throughout the day Thursday.
Viral video spreading misinformation about storm debunked by emergency officials
A widely circulated video is misleading Californians about the coming storm, California emergency officials said.
“This video has received more than half a million views and is misleading Californians about a storm of epic proportions that they say is about to hit our state,” a spokesperson for the California Office of Emergency Services told KABC-TV.
“Although California has a long history of flooding, residents have nothing to fear as long as they take some basic steps to be prepared,” the OES spokesperson said.
What is an atmospheric river?
Atmospheric rivers capture water vapor from warm, moist air in tropical regions and then drop the water to the ground in cold regions as rain or snow. Atmospheric rivers are part of Earth's ocean water cycle, and are closely linked to water supply and flood risk, the National Oceanic and Atmospheric Administration says.
These bands of water vapor, exposed by clouds, extend thousands of miles from the tropics into the western United States, are 250 to 375 miles wide, and provide fuel for heavy rains and snowstorms that can cause flooding along the West Coast.
A 2017 study said these “rivers in the sky” are responsible for up to 65% of heavy rain and snow in the western United States. On average, up to 50% of annual precipitation on the West Coast occurs in a few weather-river events.
Contributing: Doyle Rice, USA TODAY; Associated Press
