12 Jan 2023 | 09:24 AM UTC
US: Further adverse weather forecast across much of California through at least Jan. 15 /update 5
Heavy rainfall and mountain snowfall forecast across much of California, US, through Jan. 15. Flooding and associated disruptions ongoing.
Event
An atmospheric river is forecast to continue bringing excessive rainfall and heavy mountain snow across much of California through at least Jan. 15. The ongoing heavy rains are forecast to shift over northern California through early Jan. 14, with northwestern California receiving the highest amounts of rainfall. After which, another surge of heavy rainfall is likely over most of California through at least Jan. 15.
Heavy rainfall across most of California since Jan. 1 has resulted in at least 18 fatalities. At least one person remains missing; search operations are ongoing. Officials declared a state of emergency across California and evacuation orders and alerts remain in place over portions of Monterey, Sacramento, and Santa Cruz counties due to the risk of flooding and landslides. Reports indicate that more than 130 homes in Santa Barbara County are significantly damaged.
Flooding and landslides have caused road closures across parts of the state, including sections of Highway 1, and snow chains are necessary on some mountain routes. Authorities are advising the public to limit nonessential travel over the coming days due to adverse weather conditions. As of early Jan. 12, more than 40,000 people across California are without power, predominantly in central California and along coastal areas.
As of early Jan. 12, the National Weather Service (NWS) has issued flood and flash flood watches and warnings across parts of northwestern and central California. Winter weather advisories are in place over mountainous areas, while high wind warnings are in place across the northwestern part of the state.
The NWS's Weather Prediction Center (WPC) has warned of a "Slight Risk" (Level 2 on a four-tier scale) of excessive rainfall over portions of the northern California coast Jan. 12, over portions of the northern California coast and adjacent mountains Jan. 13, and over portions of northern and central California Jan. 14. Authorities will likely update and possibly extend the coverage of weather alerts over the coming days as the storm progresses and weather conditions change.
Sustained heavy rainfall could trigger flooding in low-lying communities near rivers, streams, and creeks. Urban flooding is also possible in developed areas with easily overwhelmed stormwater drainage systems. Sites downstream from large reservoirs or rivers may be subject to flash flooding after relatively short periods of intense rainfall. Landslides are possible in hilly or mountainous areas, especially where heavy rainfall has saturated the soil. Authorities could issue mandatory evacuation orders for flood-prone communities over the coming days. Disruptions to electricity and telecommunications services are possible where severe weather impacts utility networks.
Precipitation will likely 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.
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.
Severe weather will also likely trigger flight delays and cancellations at airports across the affected 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 could block regional rail lines; freight and passenger train delays and cancellations are likely in areas that see heavy rainfall and potential track inundation.
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.
