Latest atmospheric river brings “catastrophic” flood risk

California faces another atmospheric flow event on Tuesday that forecasters warn will bring heavy rains, widespread flooding and mountain snow to much of the state through Wednesday — as officials continue to do answer until the last deadly storm.

The big picture: As heavy rain fell early Tuesday, officials warned the latest atmospheric flow could “hammer” areas devastated by flooding in the earlier storm.

• The National Weather Service (NWS) issued a “high risk” forecast of excessive rain, the highest of its magnitude and a relatively rare designation.
• The NWS is warning of “significant to locally catastrophic flooding impacts” below 5,000 feet, with the heaviest rains gradually moving down the coast from the San Francisco Bay Area into the southern Sierra Nevada foothills on Tuesday.
• “Severe, widespread flash flooding is expected,” the agency said in an online forecast discussion. “Areas not normally affected by flash floods are being inundated. Life and property are in grave danger Tuesday through Wednesday.”

Threat Level: The weather bureau, in another discussion, noted that the recent atmospheric flow contains an unusually high amount of moisture and will remain parked over the same areas for an extended period of time.

• Forecasters also warned of rapid snowmelt raising water levels in rivers and streams.
• One of the places meteorologists were keeping a close eye on is Monterey County, where the California National Guard was helping 56 people saved after the dam of the Pajaro river breached early Saturday.
• Patrick Ayd, a meteorologist with the National Weather Service, told the Los Angeles Times, “We have very saturated soils that will make us even more vulnerable to flooding.”
• Damaging winds and power outages are likely, particularly in central California. These winds are predicted to play a bigger role in this next storm than the one that hit late last week.

Game Status: Local schools and streets were closed and evacuation assignments And warnings were in effect for communities along Pajaro and Monday other rivers because of rising flood and the risk of further flooding.

• Luis Alejo, Chairman of the Board of Directors of Monterey County, tweeted Monday night that a fracture area along the Pajaro dike “had grown from 120 to 400 feet wide” but a temporary wall of rock and sand “will prevent the fracture from widening” and “slow the flow water to the Pajaro community.”
• Steady rain along the Sacramento River kept water levels rising Sunday before more rain was forecast, officials in Calaveras County, southeast of Sacramento, said. issued an emergency road closure due to flooding.
• The Bay Area experienced several storm-related road closures and the Oakland Zoo called it would be closed on Tuesday due to forecasts of heavy rain and wind.

In the meantime, The southern Sierra Nevada appears to have recorded its greatest snow cover on record — more than 250% above the seasonal average, according to the California Department of Water Resources.

• The UC Berkeley Central Sierra Snow Lab reported Monday saw an additional 13.2 inches of snow fall within 24 hours, marking the “third snowiest winter on record” at the Sierra Nevada lab.
• The lab has recorded 651 inches since Oct. 1 and expects an additional 18 to 30 inches of snow through Tuesday.

What we observe: Where the heaviest rains will occur Tuesday through Wednesday, which will determine the locations of the worst impacts.

• This atmospheric flow of the “Pineapple Express” is expected to see heavy rain and high-altitude snow through Wednesday.
• The humidity for this particular storm comes from near Hawaii.

Context: Atmospheric fluxes are strong because narrow currents in the air can carry massive amounts of water vapor thousands of miles, from the tropics to mid- and northern latitudes — and they’ve hit California more than a dozen times this year.

Editor’s Note: This story has been updated throughout with new forecast details.