A cold trough slides down the British Columbia coastline as the surface low tracks into the British Columbia Interior. A band of increasing moderate to heavy rain and snow impacts the Pacific Northwest as the surface cold front drops SE. The heaviest precipitation will be in the central and southern Washington Cascades and Paradise with significant rainshadowing for the eastern Olympics and Puget Sound lowlands. Snow levels hover in the 3500-4500 ft range for most of the area with little change throughout the day. WSW winds have been moderate to strong along the east slopes of the Cascades, but have generally lagged model expectations thus far. Widespread moderate ridgeline winds should develop with more meteorological forcing as the front approaches.
The cold front pushes through the Olympics and Mt Baker areas around 3-4 PM, moving through the central and southern Washington Cascades from 4-7 PM, and pushes through Mt Hood overnight. This pushes the heaviest precipitation southward and ultimately out of the picture as precipitation becomes showery. Snow levels drop rapidly behind the front with a shift to snow levels below 1500 ft in all areas by Monday morning as moderate snow showers continue in most areas. Convergence bands likely set up near Stevens Pass and snow ratios should be closer to 15 to 1.
On Monday, a cold trough passes over the region with light to moderate ridgeline winds out of the W or WNW. It will be cold with snow levels between sea level and 1000 ft in most areas. Convergence enhancement will create locally heavy snow at times in areas from Snoqualmie Pass to Mt Baker.
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
Increasing light rain and snow (moderate to heavy for the western Olympics). Light to moderate ridgeline winds.
Sunday
Night
Light snow showers. Plummeting temperatures. Light to moderate ridgeline winds become light.
Sunday
Increasing moderate to heavy rain and snow (very heavy western part and highway 20). Moderate ridgeline winds develop.
Sunday
Night
Decreasing moderate snow showers becoming light.
Sunday
Increasing heavy rain and snow. Increasing moderate ridgeline winds with strong gusts.
Sunday
Night
Decreasing moderate to locally heavy snow showers.
Sunday
Increasing light rain and snow becomes moderate to heavy in the afternoon. Increasing moderate ridgeline winds with strong gusts.
Sunday
Night
Moderate to heavy snow transitions to light to moderate snow showers. Decreasing moderate ridgeline winds with strong gusts.
Sunday
Increasing moderate to heavy rain and snow. Increasing moderate ridgeline and light to moderate W wind at the Pass.
Sunday
Night
Decreasing moderate to heavy snow showers and convergence. Decreasing moderate ridgeline and light to moderate W wind at the Pass.
Sunday
Increasing moderate to heavy rain and snow. Increasing moderate ridgeline and light to moderate W wind at the Pass.
Sunday
Night
Decreasing moderate to heavy snow showers and convergence. Decreasing moderate ridgeline and light to moderate W wind at the Pass.
Sunday
Increasing light to moderate or heavy rain and snow. Increasing moderate ridgeline winds possibly becoming strong.
Sunday
Night
Decreasing light snow showers. Decreasing moderate to strong ridgeline winds.
Sunday
Increasing light to moderate rain and snow. Increasing moderate to strong ridgeline winds.
Sunday
Night
Decreasing moderate snow showers become light.
Sunday
Increasing light rain and snow. Increasing moderate ridgeline winds.
Mostly sunny to start, with increasing clouds. Light to moderate rain and snow develop by mid-afternoon. Increasing moderate to strong ridgeline winds.
Sunday
Night
Moderate to heavy rain and snow. Decreasing moderate to strong 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).