A low center moves east of the Cascades by Monday evening with WNW ridgeline winds and mountain-enhanced rain/snow showers in its wake as weak ridging builds offshore. The ridgeline winds should be in the moderate range near and east of the Cascade Crest with strong winds for Mt. Hood. Rain and snow decreases and becomes showery overnight as cooling brings snow levels back down below Snoqualmie Pass level during the evening hours.
Winds shift to the WSW on Monday as temperatures gradually increase at mid and upper elevations. Increasing moisture spills over the top of the ridge into the west slopes of the Cascades ahead of a stronger frontal system drifting southward down the coast of British Columbia. Snow levels should hover near 3000 ft.
Moderate to heavy rain and snow increase as the moisture-laden frontal boundary moves into NW Washington Monday night, focusing the heavier precipitation on the Olympics and west slopes of the Cascades north of I-90. Snow levels hover between 3000-3500 ft. Moderate to heavy rain and snow will cover the region as the frontal boundary moves through the region from N to S on Tuesday. Mt. Baker could pick up 3" of water equivalent Monday night through Tuesday. Snow levels are likely to be near or just above Snoqualmie Pass through this period, drastically limiting accumulations.
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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Sunday
Night
A few flurries in the evening, then very light rain and snow showers focusing on the western slopes of the Olympics.
Monday
Periods of light rain and snow, mainly on the W slopes of the Olympics.
Sunday
Night
Decreasing light rain and snow showers.
Monday
Light rain and snow.
Sunday
Night
Light to moderate rain and snow showers, heaviest in convergence (southern part) during the evening hours. Shower activity decreases overnight.
Monday
Light to occasionally moderate rain and snow.
Sunday
Night
Decreasing light rain and snow showers. Moderate to strong ridgeline winds near the Cascade Crest.
Monday
Moderate rain and snow at Paradise with light rain and snow at Crystal and White Pass.
Sunday
Night
Light to moderate snow showers and convergence in the evening with decreasing light showers overnight. Moderate ridgeline and light to moderate W wind at the Pass.
Monday
Light to moderate rain and snow. Moderate ridgeline and decreasing light wind at the Pass.
Sunday
Night
Light to moderate snow showers and convergence in the evening with decreasing light showers overnight. Moderate to occasionally strong ridgeline and light to moderate W wind at the Pass.
Monday
Moderate rain and snow. Moderate ridgeline and decreasing light to moderate wind at the Pass.
Sunday
Night
Very light snow showers or flurries near the Cascade Crest. Moderate ridgeline winds.
Monday
Periods of light snow, increasing. Moderate ridgeline winds.
Sunday
Night
Decreasing light rain and snow showers. Moderater ridgeline winds.
Monday
Increasing light rain and snow. Moderate ridgeline winds.
Sunday
Night
Decreasing light snow showers or flurries near the Cascade Crest. Moderate ridgeline winds.
Monday
Mostly cloudy with very light rain or snow possible near the Cascade Crest. Moderate ridgeline winds.
Sunday
Night
Moderate rain and snow becoming light and showery overnight. Decreasing strong ridgeline winds.
The strong cooling and W flow that started Tuesday afternoon should continue overnight, bringing 24 hours of below-average temperatures. Heavy snowfall tapers to light showers and convergence overnight. Light snow showers decrease or end from south to north with weak ridging allowing for a gradual increase in temperatures on Wednesday. A warm front may clip the Olympics for some light rain or snow Wednesday night. Most models keep the ridge over the area through Thursday with a mainly dry solution, but there's a chance that a trough and active weather return on Thursday.
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).