A long-duration significant winter storm unleashes across the Pacific Northwest through the next 24 hours.
The front progressed into the southern Cascades Thursday night, but a moist flow continues on a brisk WSW flow. The northern half of the forecast region can expect moderate rain and snow showers that will be locally heavy in convergence in the vicinity of Snohomish County. Further south, the stalled front will bring more widespread precipitation that could become heavy in the afternoon with a shortwave feature. Expect convection, particularly in the late afternoon and evening hours. Winds will be mi the moderate range for areas exposed to WSW winds.
Winds increase overnight near and east of the Cascade Crest with shower activity and snow levels dropping below 3000 ft. A convergence drops southward toward Stevens Pass and could deposit significant snowfall.
Expect a relative break on Saturday as winds die down and snow showers taper early in the day. Saturday afternoon temperatures will moderate but isolated snow showers will cool things down when precipitation arrives.
Weather Forecast
Olympics
West North
West Central
West South
Stevens Pass
Snoqualmie Pass
East North
East Central
East South
Mt. Hood
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Friday
Light rain and snow showers increase and become more convective in the afternoon.
Friday
Night
Decreasing light rain and snow showers.
Friday
Decreasing moderate rain and snow showers. Moderate ridgeline winds in areas near the Cascade Crest.
Friday
Night
Decreasing mostly light rain and snow showers.
Friday
Moderate rain and snow showers. Moderate ridgeline winds.
Friday
Night
Decreasing moderate snow showers (locally heavy in strong convergence bands). Decreasing moderate ridgeline winds.
Friday
Light to moderate snow becomes moderate to heavy in the afternoon. Moderate ridgeline winds may be strong near the Cascade Crest.
Friday
Night
Decreasing moderate rain and snow showers. Decreasing moderate winds may be strong at times near the Cascade Crest.
Friday
Moderate rain and snow showers may become steady in the afternoon. Moderate ridgeline and light W wind at the Pass.
Friday
Night
Moderate snow showers transition to heavy snow at times in strong convergence. Moderate ridgeline and light to moderate W wind at the Pass.
Friday
Moderate rain and snow showers may become steady in the afternoon. Moderate ridgeline and light to moderate W wind at the Pass.
Friday
Night
Decreasing moderate snow showers. Moderate ridgeline and light to moderate W wind at the Pass.
Friday
Light to occasionally moderate rain and snow showers. Moderate ridgeline winds.
The NWAC program is administered by the USDA-Forest Service and operates from the National Weather Service Forecast Office in Seattle. NWAC services are made possible by important collaboration and support from a wide variety of federal, state and private cooperators.
The 5000’ temperature forecast does not imply a trend over the 12 hr period and only represents the max and min temperatures within a 12 hr period in the zone. The 6-hr snow level forecast, the forecast discussion, and weather forecast sections may add detail regarding temperature trends.
The snow level forecast represents the general snow level over a 6 hr time period. Freezing levels are forecast when precipitation is not expected.
*Easterly or offshore flow is highlighted with an asterisk when we expect relatively cool east winds in the major Cascade Passes. Easterly flow will often lead to temperature inversions and is a key variable for forecasting precipitation type in the Cascade Passes. Strong easterly flow events can affect terrain on a more regional scale.
Ridgeline winds are the average wind speed and direction over a 6 hr time period.
The wind forecast represents an elevation range instead of a single elevation slice. The elevation range overlaps with the near and above treeline elevation bands in the avalanche forecast and differs per zone.
Wind direction indicates the direction the wind originates or comes from on the 16-point compass rose.
Water Equivalent (WE) is the liquid water equivalent of all precipitation types; rain, snow, ice pellets, etc., forecast to the hundredth of an inch at specific locations. To use WE as a proxy for snowfall amounts, start with a snow to water ratio of 10:1 (10 inches of snow = 1 inch WE). Temperatures at or near freezing will generally have a lower ratio (heavy wet snow) and very cold temperatures can have a much higher ratio (dry fluffy snow).