CW3E AR Update: 29 January 2025 Outlook

January 29, 2025

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Pair of Atmospheric Rivers Forecast to Bring Heavy Precipitation to US West Coast

Two atmospheric rivers (AR) are forecast to make landfall in quick succession over Northern and Central California resulting in potentially heavy precipitation.
The first AR is forecast to make landfall late Thu 30 Jan over the Pacific Northwest and propagate down the coast into Sat 1 Feb.
The second AR is forecast to develop near Hawaii within a tropical moisture export (TME) and propagate toward the US West Coast on Fri 31 Jan.
There is much uncertainty between the ECMWF and GFS regarding landfall location and timing of the second AR, impacting where the highest precipitation is forecast to fall.
The ECMWF is forecast highest precipitation totals over Northern California Coast Ranges while the GFS maximum is over the Northern and Central Sierra Nevada.
The NWS Weather Prediction Center forecast is similar to the ECMWF, with 6–12 inches of precipitation forecast over the Northern California Coast Ranges and the Northern Sierra Nevada during the next 7 days.
The Weather Prediction Center has issued a slight risk Excessive Rainfall Outlook (ERO) (level 2 of 4, 15% chance of flooding) has been issued over Del Norte, Humboldt, and Mendocino Counties for day 4 (precipitation ending 4 AM PT 2 Feb)
Stream levels are forecast to rise in southern Oregon and Northern and Central California, with the largest likelihood of flooding in Northern California.
Snowfall accumulations of 8–18 inches over the Cascades, 2–6 inches over the Sierra Nevada and 6-18 inches over the Klamath Mountains are forecast over the next three days.