A ridge of high pressure just offshore continues to build and expand into our region on Tuesday. It will bring mild temperatures to middle and upper elevations through the next 36 hours as the ridge transits W to E across our region. Easterly gradients drive increasing E winds through the mountain gaps through Tuesday night. With a cold pool strengthening east of the Cascades, expect cool temperatures and stratus below around 4500 ft at places like Snoqualmie Pass (and perhaps Stevens as well). Inversions were strong at Washington Pass (20F) and should continue as milder air continues to filter in above the strengthening cold pool.
A weakening frontal system brings increasing SSW winds and high clouds Tuesday night into Wednesday. Expect moderate ridgeline winds in many areas that are favored by southerly or E flow. These areas include Mt Baker, the Olympics, and the mountain gaps.
Freezing levels peak on Wednesday at around 8000-10000 ft for locations above or west of the cold air pool.
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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Tuesday
Mostly sunny with increasing high clouds. Mild. Light ridgeline winds.
Tuesday
Night
Mostly clear with increasing thin, high clouds. Multiple freezing levels. Increasing moderate ridgeline winds.
Tuesday
Mostly sunny with a few high clouds in the afternoon. Mild. Light ridgeline winds.
Tuesday
Night
Mostly clear with increasing thin, high clouds. Multiple freezing levels. Increasing moderate ridgeline winds.
Tuesday
Mostly sunny with a few high clouds in the afternoon. Mild. Light ridgeline winds.
Tuesday
Night
Mostly clear with increasing thin, high clouds. Multiple freezing levels. Increasing light to moderate ridgeline winds.
Tuesday
Mostly sunny with a few high clouds in the afternoon. Mild. Increasing light to occasionally moderate ridgeline winds.
Tuesday
Night
Mostly clear with increasing thin, high clouds. Multiple freezing levels. Increasing light to moderate ridgeline winds.
Tuesday
Mostly sunny with a few high clouds in the afternoon. Multiple freezing levels. Increasing light to occasionally moderate ridgeline winds. Increasing light E winds at the Pass.
Tuesday
Night
Mostly clear with increasing thin, high clouds. Multiple freezing levels. Increasing moderate ridgeline winds. Increasing moderate E winds at the Pass.
Tuesday
Mostly sunny up high with low cloud streaming through at pass level. Multiple freezing levels. Increasing moderate ridgeline winds. Increasing light to moderate E winds at the Pass.
Tuesday
Night
Mostly clear with increasing thin, high clouds. Low cloud streaming through at pass level. Multiple freezing levels. Increasing moderate ridgeline winds. Increasing 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).