The Thanksgiving week's most significant storm moves through Saturday night into Sunday. The trough responsible for the storm has southerly upper-level winds ahead of it with an abrupt shift to NW flow aloft on the backside. Light to moderate rain and snow increases across southern Washington, the Olympics, and Mt Hood areas Saturday evening with snow levels starting around 6000 ft in areas west of the Cascade Crest. Rain and snow spread NE throughout the Cascades overnight. Easterly flow ahead of the front should maintain snowfall at Stevens and Washington Passes, but Snoqualmie should start as rain at pass level. The front ushers in moderate to strong post-frontal westerly ridgeline winds and moderate post-frontal rain/snow showers at rapidly lowering snow levels late Saturday night. The strongest winds should be in the southern Cascades volcanoes, such as on Mt. Hood. Snow levels should drop to and linger around 3000 ft most of the day on Sunday. Bands of convergence enhancement likely form over the Mountain Loop late Saturday night, shifting southward toward Stevens Pass early Sunday, followed by a shift to Snoqualmie Pass to Crystal from mid-morning onwards
A rebounding offshore ridge quickly tapers precipitation late Sunday into the evening hours. Storm totals should range from 3-8" at most trailhead locations. Paradise, Timberline, and Mt Hood Meadows can anticipate 6-12" of snow with upwards of a foot likely above 6000 ft on the southern Cascades volcanoes.
Temperatures will be cool as skies clear Sunday night. With the ridge squarely over the region on Monday, expect widespread sunshine. After a chilly start, temperatures skyrocket and freezing levels rise to 9000-12000 ft by the afternoon for many areas. However, a cool pool remains E of the Cascades with E flow keeping the passes hovering near freezing with low-level fog possible.
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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Saturday
Night
Increasing light rain and snow in the evening, becoming moderate at times overnight. Lowering snow levels. Moderate ridgeline winds with strong gusts.
Sunday
Decreasing light snow showers with frequent sun breaks in the afternoon. Moderate ridgeline winds become light by the afternoon.
Saturday
Night
Cloudy with light rain and snow developing and becoming moderate in the early morning hours. Light ridgeline winds become moderate overnight.
Sunday
Moderate snow showers in the morning become light. Decreasing light to moderate ridgeline winds.
Saturday
Night
Light rain and snow develop in the late evening and become moderate at times overnight. Elevated snow levels to start, lowering overnight. Light ridgeline winds increase into the moderate range.
Sunday
Moderate snow showers (heaviest in convergence) in the morning hours, become light in the afternoon. Decreasing moderate ridgeline winds.
Saturday
Night
Increasing light rain and snow in the evening with moderate rain and snow overnight (possibly heavy at times for Paradise). Light ridgeline winds become moderate overnight.
Sunday
Moderate to occasionally heavy snow showers at Paradise with light to occasionally moderate snow showers at Crystal and White Pass. Decreasing moderate to occasionally strong ridgeline winds.
Saturday
Night
Light snow develops in the late evening hours and becomes moderate in the early morning hours and could mix with rain briefly. Light ridgeline winds become moderate. Decreasing light E winds at the Pass switching W after midnight.
Sunday
Decreasing moderate snow showers, locally heavy at times in convergence during the morning hours. Decreasing moderate to occasionally strong ridgeline winds.
Saturday
Night
Light rain/snow with a slight chance of freezing rain develops in the evening hours and becomes moderate in the early morning hours y. Light ridgeline winds become moderate with strong gusts. Decreasing light to moderate E winds at the Pass switching W after midnight.
Sunday
Decreasing moderate rain and snow showers, locally heavy at times in convergence. Decreasing moderate to occasionally strong ridgeline winds. Snow levels near or slightly below the Pass.
Saturday
Night
Cloudy in the evening with a period of light to moderate snow overnight. Increasing light ridgeline winds.
Sunday
Light snow showers tapering to flurries by the afternoon with increasing sun breaks. Decreasing light to moderate ridgeline winds become light.
Saturday
Night
Light to occasionally moderate rain, snow with a slight chance of a wintry mix. Light ridgeline winds become moderate overnight.
Sunday
Gradually decreasing light snow showers with increasing sun breaks throughout the day. Decreasing moderate to strong ridgeline winds.
Saturday
Night
Light to occasionally moderate rain and snow. Light ridgeline winds become moderate overnight.
Sunday
Gradually decreasing light snow showers with increasing sun breaks throughout the day. Decreasing moderate to strong ridgeline winds.
Saturday
Night
Light rain and snow become moderate from the late evening onwards. Lowering snow levels. Ridgeline winds increase from the light to the strong range.
The ridge shifts slightly E of the area Monday night, enabling low-level winds to shift back westerly. A weakening front approaches the coastline on Tuesday bringing increasing clouds and cooling temperatures to the region. The front should bring a period of light rain and snow Tuesday night into early Wednesday with very light, isolated showers possible into the afternoon. Snow levels should be slightly above seasonal norms.
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).