After an unusually dry January, a powerful atmospheric river known as the Pineapple Express is set to bring heavy rain, snow, and strong winds to central and northern California in the coming days.
This weather system, which originates near Hawaii and carries warm, moisture-laden air, is expected to bring multiple waves of precipitation, with some inland areas receiving 10-20 inches (250-500mm) of rain and up to 6 feet (about 2 meters) of snow in the Sierra Nevada mountains.
While Northern California braces for heavy rainfall, residents in the southern regions are hoping for some much-needed moisture.
Since early January, large wildfires have ravaged parts of Los Angeles and San Diego counties, destroying over 16,000 structures and forcing hundreds of thousands to evacuate temporarily. Nearly 54% of the state remains under official drought conditions, with some of the worst-hit areas being those affected by the recent fires.
Pineapple Express
According to a report by the BBC, the Pineapple Express is a type of atmospheric river—a narrow, fast-moving “river in the sky” that carries significant moisture over long distances. The warm air and high humidity it transports from the Pacific result in heavy rainfall when it reaches land.
Atmospheric rivers vary in size and intensity, but those with the highest levels of water vapor and strongest winds can cause extreme rainfall and flooding, as noted by the National Oceanic and Atmospheric Administration (NOAA). The NOAA explains that these atmospheric rivers are long, narrow bands in the atmosphere that move large amounts of water vapor from the tropics. While their size and strength can vary, on average, they carry a volume comparable to the flow of the Mississippi River at its mouth, with exceptionally powerful ones transporting up to 15 times that amount. Upon reaching land, they typically release this moisture as rain or snow, often covering a large area as they move inland.
AccuWeather meteorologist Matt Rinde explained to Newsweek that the “Pineapple Express” refers to an atmospheric river originating in the tropical Pacific, usually near Hawaii. “This carries a considerable amount of liquid that gets ‘squeezed out’ as it reaches land,” he said.
These systems typically form alongside large storm systems in the upper atmosphere and occur relatively frequently, ranging from a few times to several times a year, he added.
Flooding & Mudslides: Intense rainfall is predicted to lead to flooding, especially in low-lying areas and near rivers. The dry, hardened ground from previous droughts heightens the risk of mudslides and landslides.
Heavy Snowfall: The Sierra Nevada is expected to receive up to 6 feet of snow, particularly between Yosemite and Lake Tahoe, increasing the likelihood of avalanches.
Strong Winds & Power Outages: Powerful winds of 90-100 mph (145-160 km/h) will accompany the system, and combined with heavy, wet snow, could bring down power lines and result in widespread outages.
When will it end?
A forecast map from AccuWeather, shared with Newsweek, showed that parts of Northern California are expected to experience heavy rain and snow from Friday night through Monday. The most severe conditions are anticipated through Tuesday night, with central and northern California bearing the brunt of the impact. By Wednesday, the storm is expected to weaken, potentially bringing lighter rainfall to southern California, including Los Angeles.
Although atmospheric rivers account for up to 50% of California’s annual rainfall, stronger events like this one can cause significant damage. Scientists warn that climate change may intensify these systems in the future, leading to increased rainfall at lower elevations, higher flooding risks, and more severe storms.
Residents are urged to stay alert, follow weather updates, and prepare for possible flooding, road closures, and power outages.
