The last in a series of winter storms impacts the region Monday and Tuesday. Post-frontal showers on SW flow became scattered on Monday morning but continued for some parts of the west slopes of the Cascades. These showers generally continue to diminish through the morning hours. A strong frontal system associated with a pronounced offshore trough approaches the coast in the afternoon, spreading increasing light and, in some cases, moderate rain and snow throughout the region. Snow levels rise from around 2000 ft in the morning to 2500-3500 ft. Ridgeline winds shift more to the SSW and generally increase but remain in the light to moderate range.
The front arrives Monday evening with moderate to heavy rain and snow, moderate to occasionally strong SSW ridgeline winds, and a touch of warming. Light E flow through the passes may insulate the Pass level from the subtle warming, but expect snow levels to rise above pass level following the late evening frontal passage and before temperatures cool. Moderate snow showers continue through Tuesday for the west slopes of the Cascades. Models indicate the potential for locally heavy snowfall in a convergence band forming around Mt Baker early Tuesday and dropping southward as the day progresses. This band could drop as far southward as Stevens Pass by the end of the day. Snow levels lower from around 3000 to 2500 ft while winds generally remain steady or decrease in the light to moderate range, accelerating east of the Cascades Crest.
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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Monday
Light (but locally intense) rain and snow showers, then increasing steady light to moderate rain and snow (moderate to heavy in southern and eastern Olympics). Increasing moderate ridgeline winds.
Monday
Night
Moderate rain and snow (heavy southern and eastern Olympics) transitioning to showers. Decreasing moderate ridgeline winds.
Monday
Light rain and snow showers in the morning, then increasing steady light to moderate rain and snow. Increasing moderate ridgeline winds.
Monday
Night
Heavy rain and snow in the evening, then decreasing into the moderate range overnight. Decreasing moderate to occasionally strong ridgeline winds.
Monday
Light rain and snow showers in the morning, then increasing steady light rain and snow. Light to moderate ridgeline winds.
Monday
Night
Moderate to heavy rain and snow in the evening, moderate snow showers and convergence overnight. Moderate ridgeline winds.
Monday
Light rain and snow showers in the morning, then increasing steady light to moderate rain and snow in the afternoon. Light to moderate ridgeline winds.
Monday
Night
For the volcanoes: Moderate to heavy rain and snow in the evening, then decreasing moderate snow showers and convergence overnight. For Crystal and White Pass: Moderate rain and snow in the evening, then light snow showers overnight. Moderate ridgeline winds.
Monday
Occasional light rain and snow showers in the morning, then increasing steady light rain and snow in the afternoon. Light ridgeline and light W wind shifting E at the Pass by mid-morning.
Monday
Night
Moderate rain and snow in the evening, then light snow showers overnight. Light to moderate ridgeline and light E wind switching W at the Pass overnight.
Monday
Occasional light rain and snow showers in the morning, then increasing steady light rain and snow in the afternoon. Increasing light ridgeline and light W wind shifting E at the Pass by mid-morning.
Monday
Night
Moderate rain and snow in the evening, then light snow showers overnight. Light to moderate ridgeline and light E wind switching W at the Pass overnight.
Monday
Occasional light rain and snow showers in the morning, then increasing steady light rain and snow in the afternoon. Light to moderate ridgeline winds.
Monday
Night
Light to moderate rain and snow in the evening, then light showers overnight. Light to moderate ridgeline winds.
Monday
Occasional light rain and snow showers in the morning, then increasing steady light rain and snow in the afternoon. Moderate ridgeline winds.
Monday
Night
Light to moderate rain and snow in the evening (potentially heavy near the Cascade Crest), then light showers overnight. Moderate ridgeline winds.
Monday
Occasional light rain and snow showers in the morning, then increasing steady light rain and snow in the afternoon. Light to moderate ridgeline winds.
Monday
Night
Light to moderate rain and snow in the evening, then light showers overnight. Moderate ridgeline winds.
Monday
Light rain and snow showers in the morning, then increasing steady light to moderate rain and snow in the afternoon. Increasing moderate ridgeline winds.
Monday
Night
Moderate to heavy rain and snow in the evening, then decreasing light to moderate snow showers overnight. Moderate to strong 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).