Second atmospheric river hits California amid ‘life-threatening’ flooding warning

A second atmospheric river-fueled storm is lashing California, threatening dangerous extreme weather in the state.

The National Weather Service warned continuous rainfall would hit over a 48-hour period in some already sodden areas across the state, including the central coast, the Los Angeles basin and in the mountain ranges.

“This heavy rainfall will bring the threat for life-threatening flash, urban, and river flooding as well as debris flows and mudslides,” the agency reported in a Sunday morning update.

Heavy snow and strong winds are expected to create impossible travel conditions in the mountains and destructive high surf along the coast.

The National Weather Service issued its first ever warning of hurricane force winds for the San Francisco area in northern California, with winds strong enough to cause flight cancellations and diversions out of San Francisco airport while, further south, the federal service gave a rare “high risk” of flash flooding warning for Los Angeles.

Wind gusts of up to 85mph were also reported along the Big Sur coast Sunday morning, as the storm pulled down power lines and created other hazards along Highway 1. More than 140,000 homes and businesses were without power across the coast of California by Sunday morning, likely due to wind impacts. Outages are expected to increase into the afternoon.

In preparation, communities tucked into mountain slopes, near surging rivers, or those close to wildfire burn scars, were put under mandatory evacuations or evacuation warnings, including in Ojai, Los Angeles and Santa Barbara. Water managers began releasing water from reservoirs that were nearing capacity in the Central Valley and Sacramento Valley, Karla Nemeth, the Director of the California department of water resources said.

The deluge comes as communities across the state were still reeling from last week’s storm, which unleashed torrents and thunderstorms on Wednesday and Thursday and tested the capacity of infrastructure.

With the grounds saturated from the first storm, the NWS warned that dangerous flash flooding would occur more quickly. “Everyone, especially those near or in south facing mountains, needs to start preparing now for possible evacuations during or even before the storm hits,” the NWS said Thursday.

California could have several more wet weeks ahead, said climate scientist Daniel Swain during a discussion of the system posted on YouTube Friday. During strong El Niño years the wet season typically peaks between February and March, he noted. “There are at least 6-7 more weeks of potential [for storms] and I would not be surprised if there was another major storm cycle at some point in that window.”

El Niño, a climate pattern associated with increased ocean temperatures in the tropical Pacific, can supercharge atmospheric rivers like the ones now creating strong storms over California with vapor that evaporates off the warmer surface waters. While there can be variability, El Niño typically delivers hotter, wet winters in California and other parts of the US south-west.

Precipitation can be a welcome sight in California, a state that spent years navigating devastating drought conditions, but timing and temperature play a big role in determining whether a storm helps or hurts. Atmospheric rivers are responsible for up to 85% of floods and destructive rains along the US west coast, but also provide up to 60% of the region’s water supply.

This year, California has gotten far more rain than snow, making a boost in water resources more difficult to capture. The snowpack, which acts as a water savings account of sorts, trickling into reservoirs, rivers and soils as it melts during drier months, stood at just 52% of average measured during the second monthly survey. Water managers are hopeful these systems will help coat the Sierra Nevada range in another thick layer.

Meanwhile, California reservoirs already stood at 115% of average going into this system, according to the California department of water resources, and in northern and southern California, rivers were already observed above flood stage. With weeks left to go in California’s wet season, and exceedingly wet conditions still in the forecast, several regions across the state had already exceeded or were nearing average precipitation levels.

Scientists have warned that this is a taste of what’s to come as the world warms, when wetter conditions with smaller snowpacks are expected to become the norm. “This tells us something about what California winters may look like increasingly in a warmer climate,” Swain said, noting that it’s both an El Niño story and a climate crisis story.