US: Flooding ongoing across California as of late March 14 /update 1

Event

Flooding and evacuations are ongoing across California as of late March 14. California remains under a state of emergency after being impacted by a series of winter storms that have struck the state over recent days and weeks. Strong winds damaged windows in a high-rise building in the San Francisco financial district evening March 14, forcing temporary evacuations and shelter-in-place orders.

Authorities in California have issued evacuation orders for more than 27,000 people across Kern, Monterey, Santa Barbara, Santa Cruz, and Sutter counties due to flooding and the risk of landslides. More than 71,600 people remain under evacuation warnings across parts of Amador, Kern, Monterey, San Benito, Santa Cruz, Stanislaus, and Ventura counties. Heavy rain over the recent days resulted in a 37 meter (120 feet) breach in the levee along the Pajaro River late March 10; authorities evacuated residents in the farm town of Pajaro. More than 450 homes in the community of Soquel, Santa Cruz County are cut off after a road collapsed. Valley Water in Santa Clara County issued a flood emergency declaration March 10, allowing the agency to take immediate action necessary to protect against or mitigate flooding. Reports indicate one fatality occurred in Oakland, California, early March 10 due to a roof collapse and another two deaths in Placer and San Bernardino counties. A boat capsized in San Diego County late March 11; at least eight people died, and search and rescue operations are underway for the remaining missing people.

Strong winds resulted in 38 flight cancellations and 345 delays at San Francisco International Airport (SFO) March 14. Further flight disruptions are possible as airlines work to clear backlogs. System-wide delays are ongoing in the Bay Area's BART transit system; high winds and fallen debris on the track are impacting services. Flooding in the Bay Area resulted in the closure of portions of Interstate 880 in Fremont and Hayward and US 101. Numerous other roads are also closed due to flooding, damage, and landslides. The Capitol Corridor rail services will bypass Fremont and Hayward stations due to a washout. More than 294,000 people are without power across western California; the worst affected is Santa Clara County, with more than 125,000 people without power.

Government Advisories
Further heavy rainfall is forecast. As of late March 14, the National Weather Service (NWS) has issued winter storm warnings for parts of northeastern and east central California. Flood watches and warnings are in effect for northwestern and northeastern California, while high wind warnings and wind advisories are in place for most of the rest of the state.

The NWS's Weather Prediction Center has warned of a moderate risk (level 3 on a four-tier scale) of excessive rainfall across parts of eastern, central, and southwestern California through early March 15. Officials could update and possibly extend the coverage of weather alerts over the coming days.

Hazardous Conditions
The storms could produce rounds of heavy precipitation (including rain and snow), strong winds, and isolated thunderstorm activity in the affected area. Where precipitation falls as rain, flash and areal flooding is possible. Such flooding is possible in low-lying communities near watercourses and other large bodies of water, as well as in urban areas with easily overwhelmed stormwater drainage systems. Sites downstream of large reservoirs may be subject to flash flooding after relatively short periods of intense rainfall.

Precipitation could fall as snow in the higher elevations over the coming days. Wind gusts could cause blowing and drifting snow; decreased visibility is likely in mountainous areas. Rain-induced landslides cannot be discounted in areas of elevated terrain; there is also the possibility of avalanches in mountainous areas where the snowpack has become unstable due to heavy snowfall. Power outages are likely throughout the affected area.

Transport
Floodwaters and related debris may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around the affected area. Flooding in urban areas could also result in significant traffic congestion. Heavy snow will likely make driving hazardous in some areas; authorities could implement temporary road closures or detours in such locations. Mountain passes and tunnels could be closed as a precautionary measure during periods of intense snowfall.

The disruptive weather will likely cause some delays and cancellations at airports in the region. Authorities may temporarily suspend port operations along the Pacific coast if strong winds trigger hazardous sea conditions, impacting freight and passenger maritime traffic. Flooding or snow could block regional rail lines; freight and passenger train delays and cancellations are possible in areas that see heavy rainfall and potential track blockages.

Disruptions triggered by inclement weather and resultant hazards, such as flooding or avalanches, could persist well after conditions have improved - it could take days before any floodwaters recede and/or officials clear debris. If there is severe damage to infrastructure, repair or reconstruction efforts may result in residual disruptions.

Advice

Monitor local media for weather-related updates and advisories. Confirm all transport reservations and business arrangements before traveling in the affected area. Seek updated information on road conditions before driving or routing shipments through areas where severe weather is forecast; plan for possible supply chain disruptions throughout the affected areas. Stay away from elevated streams, creeks, and other watercourses that are prone to flash flooding. Do not attempt to navigate flooded roadways. Exercise caution in elevated terrain due to the threat of landslides, as well as mountainous regions where avalanches pose a threat. Charge battery-powered devices in the case of prolonged electricity outages.

Resources

National Weather Service
Weather Prediction Center