Monday will be the warmest day of an extended stretch of mild weather. A warm front has progressed north of the Canadian border, leaving our region dry, within the warm sector as an atmospheric river targets southwestern British Columbia. A high pressure to our east will gain some influence over our region on Monday. As of Monday morning, most NWAC stations are reporting temperatures in the 30s, 40s, and even low 50s. Inversions have brought temperatures to just below freezing at Snoqualmie Pass East Shed and Washington Pass Base, while Camp Muir remains in the upper 20s. But these areas may rise above freezing during the day. Multiple days of strong SSW flow aloft have effectively scoured virtually all cold air out of the region. An increasing pressure difference across the Cascades will drive moderate E winds and warming at low and middle elevations west of the Cascade Crest. Expect mostly cloudy skies along with brief periods of filtered sunshine as mid and high clouds stream into the region.
The southern tip of the atmosphere clips our region Monday night with mostly light rain peaking in the evening hours. The exceptions will be Mt Baker and the southern Olympics where moderate to locally heavy rain is likely. E flow decreases with a pulse of moderate SW winds.
Monday night's system brings snow levels down to 6500-8500 ft. A warm front lifting northward should bring some light rain and very high-elevation snow from south to north. E flow increases once again, enabling the precipitation to occur on both sides of the Cascades.
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
Cloudy. Increasing moderate ridgeline winds.
Monday
Night
Cloudy with a chance of light rain. Moderate ridgeline winds.
Monday
Mostly cloudy. Increasing light to moderate ridgeline winds.
Monday
Night
Moderate to heavy rain at times. Moderate to strong ridgeline winds.
Monday
Mostly cloudy.
Monday
Night
Cloudy with periods of mostly light rain.
Monday
Mostly cloudy with filtered sunshine at times. Light to moderate ridgeline winds.
Monday
Night
Cloudy with periods of light rain. Moderate ridgeline winds.
Monday
Mostly cloudy with filtered sunshine at times. Inversion with cooler temperatures at lower elevations. Light ridgeline and E wind at the Pass.
Monday
Night
Cloudy with periods of light rain. Light ridgeline and E wind at the Pass.
Monday
Mostly cloudy with filtered sunshine at times. Inversion with cooler temperatures at lower elevations. Increasing light to moderate ridgeline and E wind at the Pass.
Monday
Night
Cloudy with periods of light rain. Moderate ridgeline and decreasing light to moderate E wind at the Pass.
Monday
Mostly cloudy with filtered sunshine at times. Inversion with cooler temperatures at lower elevations.
Monday
Night
Cloudy with periods of light rain.
Monday
Mostly cloudy with filtered sunshine at times. Inversion with cooler temperatures at lower elevations. Inversion with cooler temperatures at lower elevations.
Monday
Night
Cloudy with a chance of light rain.
Monday
Mostly cloudy with filtered sunshine at times. Inversion with cooler temperatures at lower elevations.
Monday
Night
Cloudy with a chance of light rain.
Monday
Mostly cloudy with filtered sunshine at times. Inversion with cooler temperatures at lower elevations. Light to moderate ridgeline winds.
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).