A deep upper low continues to dig southward from the Gulf of Alaska as of Wednesday morning. A front at the leading edge continues to bring precipitation to the British Columbia coastline. The edge of the high clouds associated with that precipitation extends SE as far as the Olympic Mountains and Mt. Baker areas and should relatively stationary on Wednesday, leaving most of our region under clear skies. Temperatures cooled off Tuesday night and most NWAC stations were in the 20s and low 30s. Washington Pass base presents an outlier at 9F with a moderate inversion at that location. A gradually expanding ridge across the western US in conjunction with light SW flow allows for another mild day. E flow through the mountain gaps will increase, but should not provide much cooling, making way for freezing levels in the 4500-6500 ft range by the afternoon.
A low and associated front develop off our coastline Wednesday night. Clear skies will gradually give way to increasing high clouds. Temperatures should be slightly milder with less inversion expected due to the increasing cloud cover and SSW winds increasing into the moderate range.
Clouds should lower and thicken on Thursday with moderate rain and snow reaching the Olympic Mountains during the afternoon. Temperatures will be quite mild and snow levels will hover around 5000 ft. SSW ridgeline winds should increase further into the moderate to strong range for the Olympics, Mt. Baker, and Mt. Hood.
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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Wednesday
High clouds with filtered sunshine.
Wednesday
Night
Mostly cloudy with clouds thickening.
Wednesday
High clouds with filtered sunshine.
Wednesday
Night
Mostly clear with high clouds increasing.
Wednesday
Mostly sunny with thin high clouds.
Wednesday
Night
Mostly clear with high clouds increasing.
Wednesday
Mostly sunny.
Wednesday
Night
Mostly clear with high clouds increasing.
Wednesday
Mostly sunny. Light E winds developing at the Pass.
Wednesday
Night
Mostly clear with high clouds increasing. Light to occasionally moderate E winds at the Pass.
Wednesday
Mostly sunny. Light E winds developing at the Pass.
Wednesday
Night
Mostly clear with high clouds increasing. Light to moderate E winds at the Pass.
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).