A significant winter storm continues to impact the Pacific Northwest through the weekend and into early next week. Although the cold front passed through the region on Sunday, an upper trough moving onshore Sunday afternoon will keep the snow stacking up in our mountains as snow levels drop below the major passes Sunday evening. Snow levels continue to lower through early Monday. Generally light to moderate westerly ridgeline winds will focus the moderate convective snow shower activity on the west slopes of the Cascades. As of Sunday afternoon, a heavy convergence band has formed Sunday afternoon over the Skagit Valley. This should gradually shift southward into the Mountain loop later in the day, and then over Stevens and Snoqualmie passes during the evening.
Monday morning will continue to bring periods snow showers to the west slopes and areas areas near the crest of the Cascades, with some possibility of lingering convergence zone activity in the central Cascades. Snow levels should remain low for November...mostly below 2000 ft, so expect high snow-to-liquid ratios. Snow showers gradually decrease and become mostly light on Monday afternoon and evening. However, areas from Paradise southward to Mt Hood could continue to see moderate snow showers Monday night.
Mostly light snow showers continue across the region on Tuesday as a deep upper low and rapidly intensifying surface low form in our offshore waters. By Tuesday afternoon this low is 946 mb, rivaling the strength of hurricanes. This will bring intensifying E winds through the mountain passes.
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
Night
Increasing light to moderate rain and snow showers. Generally light ridgeline winds. Gradual cooling.
Monday
Light snow showers. Light to moderate ridgeline winds.
Sunday
Night
Moderate snow showers (locally heavy at times). Generally light ridgeline winds. Gradual cooling trend.
Monday
Light to moderate snow showers. Generally light ridgeline winds.
Sunday
Night
Moderate to heavy rain and snow showers (especially in convergence from the Mountain Loop southward during the evening hours). Generally light ridgeline winds. Gradual cooling trend.
Monday
Decreasing moderate snow showers. Light to moderate ridgeline winds.
Sunday
Night
Moderate to heavy rain and snow showers, heaviest at Paradise. Light to moderate ridgeline winds. Gradual cooling trend.
Monday
Deacreasing light to moderate snow showers (heaviest at Paradise). Moderate ridgeline winds focusing on areas near the Cascade Crest.
Sunday
Night
Moderate to heavy rain and snow showers (especially in convergence from the Mountain Loop southward during the evening hours). Generally light ridgeline W wind at the Pass. Gradual cooling trend.
Monday
Decreasing light to moderate snow showers. Moderate ridgeline and light W wind at the Pass.
Sunday
Night
Moderate to heavy rain and snow showers (especially in convergence from the Mountain Loop southward during the evening hours). Light to moderate ridgeline and light W wind at the Pass. Gradual cooling trend.
Monday
Decreasing light to moderate snow showers. Moderate ridgeline and light W wind at the Pass.
Sunday
Night
Light snow showers. Generally light ridgeline winds. Gradual cooling trend.
Monday
Decreasing light snow showers focused on the western part. Generally light ridgeline winds.
Sunday
Night
Light rain and snow showers focused on the western part. Moderate ridgeline winds. Gradual cooling trend.
Monday
Light snow showers focused on the western part. Moderate ridgeline winds.
Sunday
Night
Light rain and snow showers focusing on the western part. Moderate ridgeline winds. Gradual cooling trend.
Monday
Generally light snow showers. Moderate ridgeline winds.
Sunday
Night
Moderate to heavy rain and snow showers. Moderate to strong ridgeline winds gradually decrease. Gradual cooling trend.
The aforementioned very deep low remains offshore but will bring some very intense weather to our region, particularly on Tuesday night. Expect strong and locally extreme E winds through the mountain passes and western foothills of the Cascades. Moderate upslope snowfall is likely on the east slopes of the Cascades, along with a warming trend west of the Cascade Crest, as moderate to locally heavy precipitation spreads throughout the region. East winds gradually ease on Wednesday as milder air continues to make inroads from the south. Waves of moisture continue to arrive from the SSW Wednesday night and Thursday. Throughout the period expect mostly mountain snow near and east of the Cascade Crest with rain and snow mixing further west.
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).