CW3E AR Update: 5 January 2023 Outlook

January 5, 2023

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Atmospheric Rivers Forecast to Continue to Bring Additional Precipitation to Northern and Central California

• A family of ARs (Fish et al. 2019) is forecast to make landfall beginning Friday, continuing into early next week
• The first AR is forecast to make landfall late in the day Friday 6 Jan and bring a period of IVT > 400 kg/ms into Northern and Central California
• Before AR conditions from the first AR completely dissipate, a second AR associated with a surface low-pressure system is forecast to bring a stronger pulse of IVT > 600 kg/ms to the same areas, resulting in AR 2 conditions (based on the Ralph et al. 2019 AR Scale)
• The third and strongest AR is forecast to make landfall along the coast of Northern California with IVT exceeding 750 kg/ms resulting in AR 3/AR 4 conditions in the region, although considerable uncertainty remains in the exact timing, intensity, duration, and position of this system
• The NWS Weather Prediction Center is forecasting more than 7 inches of precipitation for a broad area over coastal Northern and Central California, the Southern Cascades, and Sierra Nevada
• NWS WPC has also issued excessive rainfall outlooks for multiple days during this period, highlighting the hazard posed by additional rainfall on soils which are currently saturated
• Precipitation forecast for watersheds across Northern and Central California currently exceed 8 inches over a 7-day period, with the North Fork Feather > 10 inches over this forecast period
• The NWS California Nevada River Forecast Center has forecast streamflow to exceed flood stage at multiple locations in California in association with the precipitation from this sequence of ARs
• A period of active weather will continue for the US West Coast next week, stay tuned to CW3E for future AR Outlooks and Quick Looks
• Stay alert to official NWS forecasts, watches, and warnings at weather.gov and follow guidance from local emergency management officials

Click images to see loops of GFS IVT and IWV forecasts Valid 0000 UTC 6 January – 0900 UTC 11 January 2023

Summary provided by S. Bartlett, S. Roj, C. Castellano, J. Kalansky, and F. M. Ralph; 5 January 2023

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