A moisture-laden Pineapple Express is forecast to move toward the West Coast between December 20 and December 24, bringing a surge of warm, tropical moisture from the central Pacific. Forecasters warn this atmospheric river could deliver heavy rain, mountain snow, and gusty winds to parts of California, Oregon, and Washington. Impacts may include flooding, rising rivers, travel delays, and hazardous mountain passes as the system strengthens and moves inland ahead of the Christmas holiday.