California Faces Significant Flood Threat – Atmospheric River

 In Event News

A potent atmospheric river event – a flowing band of condensed water vapor in the atmosphere – poses a significant flood threat to California this weekend.

The atmospheric river is expected to deliver heavy rainfall and high mountain snow January 7-9.  The combination of rainfall and snowmelt presents a significant threat of flooding for parts of northern and central California. The National Weather Service says that flooding with this atmospheric river event may be the greatest of its kind since December 2005. For the latest news about this threat, please read the Weather Channel article here. 

Flood potential maps (3 and 5 day forecasts) for this event are available in EigenPrism, where users can assess the estimated impact on their portfolios, and identify the locations most at risk (login at

EigenAlert subscribers will continue to receive automated notifications as these forecasts are updated.

Insurance Brokers can use the Program Builder feature to demonstrate how a client’s insurance program will respond to this event. The feature offers a quick and easy way to flow estimated losses through current insurance program structures to test sub-limits and deductibles, and determine adequacy of limits.

Atmospheric Rivers (ARs) are relatively narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor outside of thNOAA atmospheric rivere tropics. While ARs come in many shapes and sizes, those that contain the largest amounts of water vapor, the strongest winds, and stall over watersheds vulnerable to flooding, can create extreme rainfall and floods. These events can disrupt travel, induce mud slides, and cause catastrophic damage to life and property. However, not all ARs cause damage – most are weak, and simply provide beneficial rain or snow that is crucial to water supply. For more information on atmospheric river events, see NOAA’s information page.