A ridge of high pressure centered over the Pacific Northwest on Sunday will bring mostly sunny skies and mild mountain temperatures. With descending air capping denser cold air near the surface, an inversion below 4000 ft will keep many trailhead locations cooler much of the day. The coldest low-level temperatures should be east of the Cascades and through the mountain gaps where widespread lowland snow cover has helped to form a strong but shallow cold air pool. Light E flow ushers that cold air through the mountain gaps. A few mid-level clouds over the region this morning should clear out, leaving sunny skies and a few thin high clouds. High temperatures should rise into the 40s and even low 50s throughout the region as the inversion weakens somewhat during the afternoon. The Methow Valley may be the one holdout where temperatures remain near or below freezing much of the day.
Sunday night remains mild with the ridge flattening as the southern end of a cold front approaches. Clouds lowering and thickening across Washington State and WSW ridgeline winds increase into the moderate range for many areas by the early morning hours.
The frontal passage occurs on Monday morning, bringing very light rain and a dusting of high elevation snow. A brief period of freezing rain could develop through the mountain passes if precipitation begins before winds shift westerly. Southern parts of the range may or may not see a sprinkle during the mid-day hours. Moderate WSW ridgeline winds continue much of the day and are likely to be the biggest impact with this system.
Weather Forecast
Olympics
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West Central
West South
Stevens Pass
Snoqualmie Pass
East North
East Central
East South
Mt. Hood
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Sunday
Mostly sunny with thin mid and high-level clouds decreasing early. Unseasonably mild with a low-level inversion below 4000 ft weakening as the day progresses.
Sunday
Night
Mild with high clouds lowering and thickening overnight.
Sunday
Mostly sunny with thin mid and high-level clouds decreasing early. Unseasonably mild with a low-level inversion below 4000 ft weakening as the day progresses.
Sunday
Night
Mild with high clouds lowering and thickening overnight. Strong ridgeline wind gusts likely by the early morning hours.
Sunday
Mostly sunny with thin mid and high-level clouds decreasing early. Unseasonably mild with a low-level inversion below 4000 ft weakening as the day progresses.
Sunday
Night
Mild with high clouds lowering and thickening overnight.
Sunday
Mostly sunny with thin mid and high-level clouds decreasing early. Unseasonably mild with a low-level inversion below 4000 ft weakening as the day progresses.
Sunday
Night
Mild with high clouds lowering and thickening overnight.
Sunday
Mostly sunny with thin mid and high-level clouds decreasing early. Unseasonably mild with a low-level inversion below 4000 ft weakening as the day progresses. Light E winds at the Pass.
Sunday
Night
Mild with a low-level inversion. High clouds lowering and thickening overnight. Decreasing light E winds at the Pass.
Sunday
Mostly sunny with thin mid and high-level clouds decreasing early. Unseasonably mild with a low-level inversion below 4000 ft weakening as the day progresses. Light to occasionally moderate E winds at the Pass.
Sunday
Night
Mild with a low-level inversion. High clouds lowering and thickening overnight. Light to moderate E winds becoming light at the Pass.
Sunday
Mostly sunny with thin mid and high-level clouds decreasing early. Unseasonably mild with a low-level inversion below 4000 ft weakening as the day progresses.
Sunday
Night
Mild with a strong low-level inversion. High clouds lowering and thickening overnight.
Sunday
Mostly sunny with thin mid and high-level clouds decreasing early. Unseasonably mild with a low-level inversion below 4000 ft weakening as the day progresses.
Sunday
Night
Mild with a strong low-level inversion. High clouds lowering and thickening overnight.
Sunday
Mostly sunny with thin mid and high-level clouds decreasing early. Unseasonably mild with a low-level inversion below 4000 ft weakening as the day progresses.
Sunday
Night
Mild with a strong low-level inversion. High clouds lowering and thickening overnight.
Sunday
Mostly sunny with thin mid and high-level clouds decreasing early. Unseasonably mild with a low-level inversion below 4000 ft weakening as the day progresses.
Sunday
Night
Mild with a strong low-level inversion. Strong wind gusts possible by the early morning hours. Low-level inversion.
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).