Energy & Environment ... Latest atmospheric river brings 'catastrophic' flood risk to California
Written by Rebecca Falconer
California faces another atmospheric river event Tuesday that forecasters warn will bring heavy rains, widespread flooding and mountain snow to much of the state through Wednesday — as officials continue to respond to the last deadly storm.
The big picture: As heavy rain fell early Tuesday, officials warned the latest atmospheric river could 'hammer' areas inundated by flooding in the earlier storm.
The National Weather Service (NWS) issued a 'high risk' excessive rainfall outlook, the highest on its scale and a relatively rare designation.
The NWS is warning of 'Considerable to locally catastrophic flooding impacts' below 5,000 feet, with the heaviest rains moving gradually moving down the coast from the San Francisco Bay Area, into the southern Sierra Nevada foothills Tuesday.
'Severe, widespread flash flooding is expected,' the agency stated in an online forecast discussion. 'Areas that normally do not experience flash flooding will flood. Lives and property are in great danger from Tuesday into Wednesday.'
Satellite image showing an atmospheric river taking aim at California on March 14. Darker green colors indicate the highest moisture levels. Image: NOAA.
Threat level: The weather agency noted in an another discussion that the latest atmospheric river contains an unusually high amount of moisture associated with it, and will remain parked over the same areas for extended periods.
Forecasters also warned of rapid snowmelt boosting water levels in rivers and streams.
One of the spots forecasters were watching closely is Monterey County, where the California National Guard helped rescue 56 people after the Pajaro River's levee breached early Saturday.
Patrick Ayd, a meteorologist with the National Weather Service, told the Los Angeles Times 'we have very saturated soils, which will make us even more prone to flooding.'
Damaging winds and power outages are likely, especially in Central California. These winds are predicted to be a bigger factor in this next storm than the one that hit late last week.
State of play: Local schools and roads were closed and evacuation orders and warnings were in effect Monday for communities along Pajaro and other rivers due to rising floodwaters and the threat of further inundation.
Luis Alejo, chair of the Monterey County Board of Supervisors, tweeted Monday night that a breach area along the Pajaro Levee 'had grown from 120 wide to 400 feet wide,' but a temporary rock and sand wall 'will prevent the breach from getting wider' and 'slow the flow of water into the Pajaro community.'
Steady rain along the Sacramento River saw water levels continue to rise Sunday ahead of more forecast rain, as officials in Calaveras County, southeast of Sacramento, issued an emergency road closure due to flooding.
In the Bay Area, there were several storm-related road closures and Oakland Zoo said it would close Tuesday due to forecasts of heavy rain and wind.
Meanwhile, the southern Sierra Nevada appears to have recorded its largest-ever snowpack — more than 250% above its seasonal average, according to the California Department of Water Resources.
The U.C. Berkeley Central Sierra Snow Lab reported Monday that another 13.2' of snow had fallen in 24 hours, marking the 'third snowiest winter on record' at the Sierra Nevada lab.
The lab has recorded 651' since Oct. 1 and expects another 18-30' of snow through Tuesday.
A screenshot of a tweet by climate scientist Daniel Swain noting the southern Sierra Nevada has set a new snowpack record. ... Photo: UCLA climate scientist Daniel Swain/Twitter
What we're watching: Where the heaviest rains set up on Tuesday through Wednesday, which will determine the locations of the worst impacts.
Heavy rains and high-elevation snow are expected to continue into Wednesday from this 'Pineapple Express' atmospheric river.
The moisture for this particular storm originates near Hawaii.
Context: Atmospheric rivers are potent because narrow currents in the air can carry vast amounts of water vapor thousands of miles, from the tropics to mid-and-northern latitudes — and they've lashed California on more than a dozen occasions this year.
Studies show climate change is intensifying these events since warmer air carries additional water vapor. Climate change is also yielding sharper swings between precipitation feasts and famine in California.
Editor's note: This story has been updated with new forecast details throughout.
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