13 Mar 2023 | 07:38 AM UTC
US: Adverse weather forecast over western regions through at least March 15
Heavy rainfall and snowfall forecast across parts of the western US through at least March 15. Flooding and evacuations ongoing.
Event
Heavy rainfall and higher elevation snowfall are forecast across parts of the western US through at least March 15. A frontal system over the Pacific Northwest is forecast to gradually track southward into California over the coming days, while a low-pressure system will likely track onshore into California March 14. Heavy precipitation is likely over the coming days. Additional heavy snow is forecast for the higher elevations of the Sierra Nevada. The heavy downpours could trigger flooding in low-lying areas and landslides on unstable slopes. Considerable flooding is likely along the central California coast, San Joaquin Valley, Sacramento Valley, and southern Sierra Nevada foothills through March 14. Downpours over areas of heavy snowpack will pose a threat of both flooding and avalanches due to snow melt. Strong winds could also combine with snowfall to cause blizzard conditions in areas of higher elevation.
Reports indicate one fatality 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. Authorities in California have issued evacuation orders for more than 8,500 people in Monterey County and more than 9,400 people in Kern County. Evacuation warnings remain in place for parts of Kern, Monterey, San Benito, Santa Cruz, and Stanislaus 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.
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.
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. Authorities in Nevada declared a state of emergency for Carson City and the Yomba Shoshone Tribe as well as Churchill, Douglas, Esmeralda, Elko, Eureka, Humboldt, Lyon, Mineral, Nye, Storey, Washoe, and White Pine County.
Government Advisories
Further heavy rainfall is forecast through at least March 15. As of early March 13, the National Weather Service (NWS) has issued winter storm warnings for parts of northeastern California and far northwestern Washington. Winter weather advisories are in place for western Oregon and the rest of western Washington. Flood watches are in effect for central and northern California, far southwestern Oregon, and western Nevada.
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 northern California and far southwestern Orgeon March 13 and across portions of central and southern California March 14 through early March 15. A slight risk of excessive rainfall is in place over northern California and far southwestern Orgeon through early March 13, and surrounding the moderate warning area March 14-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.
