Forecasters have warned that almost the entire state of California will endure threats by tornados, flooding, landslides, high winds, and waves as an atmospheric river is set to inundate the state with heavy rainfall. Heavy snowfall will be dumped in the higher elevations. They warned that even large urban centers such as Los Angeles have a high risk of flooding.
The rainfall began last night and will extend through Tuesday. The soils are already saturated by an earlier storm, which dumped significant rain from Wednesday through Thursday this past week.
This current storm will result in power shortages, infrastructure damage to roads, and flooding of cities. Water and sewage systems could be compromised.
Rain totals could be 3-6 inches near the coast, up to a foot inland, and last into next week. California has mountains and hills, so residents in those areas are at high risk of landslides and drowning by rainfall.
CNN, in an update report, laid out the threats to life and property:
• Rare high risk for flooding: A rare Level 4 of 4 risk of excessive rainfall was expanded Sunday to include Los Angeles, in addition to Santa Barbara and Oxnard in Southern California, with the weather prediction center warning of “life threatening flash and urban flash flooding.” Rainfall rates up to an inch per hour will bring 3 to 6 inches of rain across the area. A more widespread Level 3 risk exists for much of coastal California, including San Francisco.
• A month’s worth of rain possible in Los Angeles: In Central and Southern California, widespread rainfall totals of 3 to 6 inches are expected – more than a month’s worth of rain for most. There are indications the storm may be as strong as Tropical Storm Hilary from last August, Los Angeles Mayor Karen Bass said during a news conference Friday, and encouraged residents to take “common sense precautions.”
• Some residents told to evacuate: Mandatory evacuation orders have been issued for communities in Santa Barbara, San José and Ventura County. Officials warned residents of potential “life-threatening” floods and landslides from the atmospheric event. Several school districts in Santa Barbara County have also canceled classes on Monday due to the severe weather.
• First ever hurricane force wind warning: The National Weather Service in San Francisco on Sunday issued its first ever hurricane force wind warning since records have been kept. Wind advisories and high wind warnings are also in effect for nearly 30 million people in inland areas across nearly the entire state from Redding to San Diego.
• “Near impossible” travel in the mountains: The storm is also expected to bring significant snowfall totals in eastern California and along the Nevada border. Heavy wet snow will spread across the Sierra Nevada through Monday with accumulation rates of 2 to 3 inches per hour, according to the weather service. Dangerous wind gusts are expected to produce whiteout conditions making travel above 5000-6000 feet “near impossible,” the weather service said.
• Widespread power outages are possible: Powerful winds will also be a concern across much of California with widespread winds of 40 to 60 mph and some gusts as high as 95 mph in the foothills and mountains. This is likely to lead to downed trees and power outages Sunday and Monday, forecasters warned.
These rivers in the sky can happen anywhere on the globe, including the U.S. East Coast, but they are the main source of heavy rainfall on the U.S. West Coast. The west coasts of continents tend to have clear, uninterrupted streams of moisture.
The moist air from the tropics hits various mountain ranges on the west coast and cools as it rises. The cool air forms clouds and then creates intense precipitation on the mountains’ eastern side, said Ryan Torn, the chair of the atmospheric and environmental sciences department at the University at Albany. And the more moisture in the air, the more precipitation.
“It basically like there’s a sponge and you’re starting to just squeeze the water out of it,” Torn said. The most damaging atmospheric river, the firehose-like floods, are the ones that move down the mountain and stall in one place, he said.
This storm is expected to stall and laden with warm water. Climate change has made these naturally forming storms more frequent and able to hold more moisture content than in years past.
More rain: Experts say a warmer atmosphere in the future will hold more moisture, which could lead to more precipitation and an intensification of storms.
More frequent and more intense: Atmospheric rivers already account for nearly 90 percent of California’s flood damage. Research suggests that as temperatures warm, atmospheric rivers could occur in closer succession and drop more rainfall in a season.
Less snow: In the same way atmospheric rivers are known for bringing heavy rain to coastal and central areas, it’s crucial for bringing snow to the northern Sierra Nevada. But as temperatures warm, some research suggests that instead of snow, the rivers could bring rain to those regions too.
Some areas in Southern California, from Santa Barbara to Los Angeles have been ordered to evacuate.