Monday will be the final day with a cold trough overhead. A surface low moved into the northern Cascades overnight, increasing W winds and mountain-induced snowfall for the W slopes of the Cascades in its wake. Vancouver Island Convergence focuses on Mt Baker areas, and a Puget Sound Convergence near Stevens Pass is evident on the radar. As light to moderate ridgeline winds decrease, this more sustained snowfall should ease as we approach the late morning hours. Mid-morning and afternoon snow showers should focus more on the Mt Hood to Mt Rainier areas. Snow levels fluctuate between 0 and 1000 ft, but freezing levels are expected to rise up to 2000 ft (or slightly higher along the E slopes of the Cascades) during drier breaks in the action. Snow ratios remain high, so expect significant snowfall despite the unimpressive water numbers.
Monday evening, snow shower activity focuses on the Mt Rainier to Mt Hood areas, with a weak surface low possibly touching off some light upslope snowfall for the northern Olympics as it moves onshore. The upper trough begins to shift eastward overnight, so expect clearing skies from N to south.
Tuesday should be a cool but pleasant day. Light NW flow aloft brings mostly sunny skies in the morning with a partial cloud buildup and isolated convective snow showers in the afternoon.
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
Mostly sunny to start, then becoming mostly cloudy with light snow showers from mid-morning onwards.
Monday
Night
Cloudy with snow showers during the evening (light upslope snow for the northern Olympics). Clearing skies overnight.
Monday
Moderate snow in the morning becomes light and tapers during the afternoon. Sun breaks increasing after 2 PM.
Monday
Night
Mostly cloudy with isolated snow showers in the evening, then partly cloudy.
Monday
Moderate snow (locally heavy in convergence bands) in the morning becomes light and tapers during the afternoon with a few sun breaks.
Monday
Night
Mostly cloudy with isolated snow showers in the evening, then partly cloudy.
Monday
Light snow early with light to occasionally moderate snow showers from mid-morning onward.
Monday
Night
Light to moderate snow tapers by midnight, then partially clearing skies.
Monday
Mostly cloudy with decreasing light to occasionally moderate snow, becoming showery by the afternoon. Light to moderate ridgeline winds become light. Light W winds at the Pass.
Monday
Night
Mostly cloudy with isolated snow showers in the evening, then clearing skies overnight. Light ridgeline and W wind at the Pass.
Monday
Mostly cloudy with decreasing light to occasionally moderate snow, becoming showery by the afternoon. Decreasing light to moderate ridgeline and light W wind at the Pass.
Monday
Night
Mostly cloudy with isolated snow showers in the evening, then clearing skies overnight. Light ridgeline and W wind at the Pass.
Monday
Periods of light snow or snow showers.
Monday
Night
Partly cloudy with isolated snow showers in the evening, then clearing skies overnight.
Monday
Periods of light snow or snow showers, mainly western part. Moderate ridgeline winds decrease into the light to moderate range.
Monday
Night
Partly cloudy with isolated snow showers near the Cascade Crest in the evening, then clearing skies overnight.
Monday
Periods of light snow or snow showers, mainly western part.
Monday
Night
Decreasing isolated snow showers near the Cascade Crest.
Monday
Moderate snow showers with sun breaks possible during breaks in the shower activity. Moderate ridgeline winds with strong gusts in the morning, decreasing into the light to occasionally moderate range.
Monday
Night
Decreasing primarily light snow showers taper or end.
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).