February 4 California storm updates

Atmospheric rivers are wide-reaching plumes of moisture that act like a firehose, tapping into warm, moist air from the tropics that storms can then unload as drenching rainfall and heavy snow over land. 

These types of storms are winter hallmarks across the West Coast. Not all are harmful. Weaker atmospheric rivers deliver much-needed rainfall and snow to the region during the wettest months of the year.  

This rainfall and snow is vital to western water supplies. It fills up water reservoirs that are critical resources during dry, hot summers. 

But atmospheric rivers can quickly become more hazardous than helpful. Excessive rainfall unleashed by these potent storms increases the chances for flooding, particularly when a series of storms happen in sequence with little time to dry out between.

Last week’s atmospheric river broke multiple rainfall records across California and triggered road closures and water rescues.  

Atmospheric rivers aren’t exclusive to the West Coast. They can also impact the eastern US and happen frequently in parts of Europe, Africa, Australia and New Zealand.

The Weather Prediction Center is warning of a potentially life-threatening and dangerous flood event expected to unfold in parts of central and Southern California today.

The center has issued a rare Level 4 of 4 risk of excessive rainfall for Los Angeles, Santa Barbara and Oxnard, on Sunday. A more widespread Level 3 risk exists for much of coastal California, including San Francisco, where the National Weather Service has also issued its first-ever hurricane force wind warning for the region.

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. Los Angeles averages just 2.99 inches of rain in February, their wettest month of the year on average. In the mountains and foothills of Southern California, the weather service is forecasting up to a foot of rain.

The National Weather Service in Los Angeles warns the multi-day rain event could be dangerous and life-threatening. It could cause extensive road flooding and significant debris flow over areas that have previously burned in wildfires, possibly causing mudslides in higher terrain. Creeks and streams will rise.

Putting this rare warning into context: It’s hard to emphasize how big of a deal and how rare a Level 4 “high risk” alert is. They are issued on fewer than 4% of days per year on average, but are responsible for more than 80% of all flood-related damage and 39% of all flood-related deaths.

This event is part of an atmospheric river: a moisture plume pumping off the Pacific Ocean, feeding off warmer than average waters.

Dr. Daniel Swain, a climate scientist known for work on Western extremes, notes that heavy rain events like the one unfolding are becoming 10% more intense thanks to more fuel from a warmer climate.

The Ventura County Sheriff’s Office issued several evacuation orders for certain communities Saturday morning, along with warnings and advisories to county residents.

The orders will be in place until 5 p.m. local time Sunday, according to a release from the sheriff’s office.

The sheriff’s office also warned residents of potential landslides or debris flows, which may be caused by the amount of anticipated rain.

Residents in need of temporary shelter are encouraged to go an emergency evacuation shelter set up by the Ventura County Human Services Agency and American Red Cross.

In Santa Barbara County, an evacuation order is in place for properties along waterways and those in the area of Sycamore Creek, according to county Sheriff Bill Brown. Deputies will be going door to door to notify residents in the evacuation zones.

All county state beaches are also closed until further notice, Brown added.

Flooding is expected on streets in neighborhoods and along the highways, according to Brown, and some areas could see as much as 6 inches of floodwaters.

Several school districts in the region will also cancel classes Monday, including Santa Barbara Unified, Lompoc Unified and the Santa Maria-Bonita School District.

In addition, Santa Barbara City College announced it will have remote instruction on Monday.