California Hit by Second Atmospheric River

• 05 Feb 2024

On 4^th February, 2024, the second consecutive atmospheric river struck California, causing widespread flooding, power outages for nearly 850,000 people, and a rare warning for hurricane-force winds.

Key Points

• Impact on San Francisco Bay Area: The storm inundated streets and brought down trees and power lines across the San Francisco Bay Area. Winds reached over 60 mph (96 kph), with some areas experiencing gusts exceeding 80 mph (128 kph).
• Southern California Evacuations: In Southern California, areas at high risk for mud and debris flows, following recent wildfires, faced evacuations due to the potential for devastating flooding.
• Atmospheric River: An atmospheric river (AR) is a long, narrow band of highly concentrated water vapour in the atmosphere.
• It is often thousands of kilometers in length and can extend from the tropics to higher latitudes.
• Water Vapour Transport: ARs are responsible for transporting large amounts of water vapour, equivalent to the flow of the Amazon River.
• Connectivity: They are associated with low-level jet streams and are capable of connecting tropical moisture sources with mid-latitude regions.
• Precipitation: ARs are significant contributors to heavy rainfall and can result in intense precipitation events.
• Flooding: The concentration of moisture can lead to flooding, especially in regions with complex topography or urban areas.
• Snowfall: In colder regions, atmospheric rivers can contribute to heavy snowfall, impacting mountainous areas.