A frontal boundary will stay more or less stay stationary through the morning hours with steadier precipitation for the SW slopes of the Olympic mountains and the northwest Cascades, and more intermittent and lighter precipitation elsewhere. The frontal boundary will push inland during the afternoon, spreading more moderate precipitation to all areas near and west of the Cascade crest. Weak easterly flow will that's keeping snow levels near Pass levels this morning will give up ground as milder air moves in, with rain expected at Pass level for Snoqualmie, White and Stevens by this afternoon.
A deep upper level trough in the NE Pacific will help orient the frontal boundary from its current SW-NE position to more N-S tonight, and shift the precipitation inland. Moderate to locally heavy precipitation can be expected across all areas, along with peak warming and snow levels between 4000-5000' (higher at Mt Hood). The longwave trough will pass through Tuesday morning and push the frontal boundary to the east. This will usher in a period of post-frontal showers and strong westerly winds. The heaviest showers will likely pound the Mt Baker area in the morning, and then shift a bit south as Puget Sound Convergence zone aims into the mountains of Skagit County. Snow levels will slowly fall during the day on Tuesday to the 3000-3500' range, with slightly milder snow levels further east of the Cascade 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 to occasionally moderate rain and snow, heavier precipitation other parts of the range. Strong ridgeline winds.
Monday
Night
Light to occasionally moderate rain and snow, heavier precipitation other parts of the range. Strong ridgeline winds.
Monday
Light to moderate rain and snow, becoming moderate to occasionally heavy in the afternoon. Strong ridgeline winds.
Monday
Night
Moderate rain and snow. Strong ridgeline winds.
Monday
Light to moderate rain and snow, becoming moderate to occasionally heavy in the afternoon. Moderate to strong ridgeline winds.
Monday
Night
Moderate rain and snow. Moderate to strong ridgeline winds.
Monday
Periods of light to occasionally moderate rain and snow, becoming light to moderate rain and snow in the afternoon. Ridgeline winds becoming strong in the afternoon.
Monday
Night
Moderate rain and snow. Moderate to strong ridgeline winds.
Monday
Periods of light to occasionally moderate rain and snow, becoming light to moderate rain and snow in the afternoon. Light west winds becoming east at Pass level this morning.
Monday
Night
Moderate rain and snow. Light east winds at Pass level.
Monday
Periods of light to occasionally moderate rain and snow, becoming light to moderate rain and snow in the afternoon. Light west winds becoming east at Pass level this morning.
Monday
Night
Moderate rain and snow. Light east winds at Pass level.
Monday
Periods of light rain and snow, becoming light to occasionally moderate rain and snow in the afternoon.
Monday
Night
Light to occasionally moderate rain and snow.
Monday
Cloudy with periods of light rain and snow, becoming steadier near the Cascade crest in the afternoon.
Monday
Night
Light to occasionally moderate rain and snow. Strong ridgeline winds.
Monday
Cloudy with periods of light rain and snow, becoming steadier near the Cascade crest in the afternoon.
Monday
Night
Light to occasionally moderate rain and snow.
Monday
Cloudy with periods of light to occasionally moderate rain and snow, becoming light to moderate rain and snow in the afternoon. Ridgeline winds becoming strong.
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).