Locations Affected: United States
On 19 November, a bomb cyclone caused strong winds and torrential rainfall that disrupted infrastructure and caused widespread power outages and flooding, particularly in Washington and Northern California in the United States. Additionally, an ongoing atmospheric river event is causing rainfall and flooding risks in Northern California, Oregon, and parts of Washington in the US. The atmospheric river is adding to already saturated soil from the earlier bomb cyclone, increasing the risk of landslides and flash flooding.
Intensification of Severe Weather
The bomb cyclone is believed to have helped set the stage for the atmospheric river by pulling in tropical moisture and directing it toward the West Coast. This connection intensified the impacts of both systems, with the bomb cyclone acting as a precursor to the prolonged atmospheric river event.
Impact of the bomb cyclone:
- Strong winds of up to 70 mph have led to downed trees, blocked roads, and damage to houses. Two casualties were reported in Washington due to downed trees.
- Semi-trucks were prohibited on the highway between Carson City and Reno due to wind gusts. Interstate 05 was closed from Ashland, Oregon to the California border on 20 November.
- 252 flights were delayed and 60 were cancelled due to heavy rain and low visibility at San Francisco International Airport on 20 November.
- Until 1600 hours local time on 20 November, over 350,000 customers in Washington and 32,000 in California faced power outages
Impact of the atmospheric river:
- The storm has caused heavy rainfall and snow in Northern California on 21 November. The coasts of Northern California, Oregon, and Washington are forecast to witness persistent rainfall, flooding, and snow at higher elevations till 22 November due to the Pacific storm.
- The National Weather Service (NWS) has extended a flood watch for areas north of San Francisco until 23 November. A flood watch has also been issued for parts of southwestern Oregon through the evening of 22 November.
Weather Forecast and Potential Risks
The effects of the bomb cyclone are expected to persist, with significant impacts continuing due to the incoming storm system. Operations are ongoing to restore power in affected areas, however the disruption could last until 23 November. The atmospheric pressure is forecast to bring up to 16 inches of rainfall to parts of Northern California and southwest Oregon through 22 November. Another lighter storm is expected from 23-26 November which will bring light rain in lower elevations and heavy mountain snow. Snowfall combined with winds up to 60 mph is likely to create blizzard conditions in mountainous regions, particularly in the Cascades and far Northern California. These conditions, alongside gusty winds, are expected to increase the risk of downed trees and power outages, especially in coastal areas where snow has accumulated.
The heavy rainfall is also anticipated to heighten the threat of flash flooding, mudslides, landslides, and erosion. Travel disruptions are expected, particularly in higher elevations where snow and blizzards will severely limit visibility and road access. Flight delays and cancellations are also likely to continue, especially at airports affected by low visibility and wet conditions.
Residents in the affected areas have been urged to stay indoors during the storm and exercise caution if traveling. For real-time updates and weather advisories, it is recommended to monitor the National Weather Service website: https://www.weather.gov/.
