CW3E AR Update: 13 March 2025 Outlook

March 13, 2025

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Atmospheric River Forecast to Bring Precipitation to Oregon and Northern California

AR Summary:

An atmospheric river (AR) that made landfall late Tue 11 Mar will continue to bring rain and mountain snow to Central and Southern California today.
Another AR is forecast to make landfall over the Oregon and Northern California coasts early on Sat 15 Mar and continue through Sun 16 Mar.
This AR will bring two pulses of IVT. The second, stronger pulse of IVT will be driven by a shortwave trough and surface low-pressure system
The GEFS is forecasting AR 1-3 conditions (based on the Ralph et al. 2019 AR Scale) over the Southern Oregon and Northern California coasts for 15-17 Mar.

Precipitation Forecasts:

The NWS Weather Prediction Center (WPC) is forecasting at least 3-7 inches inches of precipitation over the Oregon Cascades, Oregon and Northern California Coast Ranges and Klamath Mountains during this event.
Freezing levels are forecast to rise across the Oregon Cascades and Klamath Mountains while remaining low over the Washington Cascades. This will lead to the highest elevations of the Oregon Cascades and Klamath still receiving some snow, but the majority of precipitation is likely to fall as rain.
The NWS is currently forecasting 12-24 inches of snowfall over the Oregon and Washington Cascades and 6-12 inches over the Klamath Mountains with the initial pulse of IVT on 15-16 Mar.

Flooding and Streamflow:

The NWS WPC has issued a marginal risk Excessive Rainfall Outlook (ERO) (level 1 of 4, 5% chance of flooding) over Western Oregon, the California Coast Ranges, Klamath Mountains and Northern Sierra Nevada.
The Northwest River Forecast Center currently forecasts five stations in Oregon to rise above minor flood stage and 12 stations across Washington and Oregon to rise above action/bankfull stage during 16-18 Mar with the incoming AR.