An active Pacific storm track/Atmospheric River will bring very heavy rainfall to the Pacific Northwest east through the northern Rockies this weekend. Showers are already ongoing through the region as an initial Pacific system moved through Saturday morning. Then, a more significant influx of moisture will arrive later Saturday, extending inland through the northern Great Basin and into the northern Rockies through Sunday.
Snowfall will remain limited to high mountain areas due to the warm Pacific air. Meanwhile, the same Pacific air will lead to heavy rainfall across the Coastal Ranges, the Olympics, and the Cascades. Isolated flooding is possible on Saturday, with a greater risk of more widespread flooding by Sunday as rainfall accumulates.
Rainfall totals of 75–100 mm (3–4 inches) are forecast for the Portland and Seattle areas, while Medford could receive up to 38 mm (1.5 inches) during the event.
Heavy snowfall is expected at higher elevations in central Idaho and northwestern Wyoming, particularly on Sunday. Runoff, combined with snowmelt from higher elevations due to warmer temperatures, will contribute to localized flooding concerns on Sunday. A Slight Risk of Excessive Rainfall is in effect for the affected regions…