CW3E AR Update: 28 February 2024 Outlook

February 28, 2024

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AR and Low Pressure-System to Produce Heavy Rain and Snow over USWC

• An atmospheric river (AR) and low-pressure system will bring widespread precipitation to the US West Coast over the next several days, including very heavy snowfall in the Sierra Nevada.
• The AR has made landfall over the PNW and is forecast to move down the USWC through Fri 1 Mar.
• Behind this AR, the associated low pressure system and a mid-level trough will help continue this precipitation event over CA through Sun 3 Mar.
• There is potential for a pulse of IVT from the central Pacific to reach the USWC and extend AR conditions and precipitation duration over northern and central CA.
• The NWS Weather Prediction Center (WPC) is forecasting significant precipitation over the next 5 days along the WA through N. CA coasts and over the Cascades and Sierra Nevada.
• The National Blend of Models (NBM) is showing very high probabilities (>90%) of snowfall exceeding 48 inches for portions of the Sierra Nevada, with accumulations forecast to potentially exceed 80 inches.
• West-WRF Ensemble meteograms are also showing very high probabilities of significant snowfall (totals > 48 inches) in the Sierra Nevada.
• The WPC Excessive Rainfall Outlooks include a Marginal Risk (level 1 of 4, or at least 5% chance) for flooding for the WA/OR/N. CA/S. CA coasts and the Sierra Nevada foothills with the the AR as it moves down the coast.
• 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 1200 UTC 28 February 2024 – 1200 UTC 3 March 2024

Summary provided by M. Steen, C. Castellano, P. Iniguez, and S. Bartlett; 28 February 2024

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*Outlook products are considered experimental

For any unfamiliar terms, please refer to the American Meteorological Society Glossary.