Mostly light rain and snow showers activity continues behind a frontal passage during the early morning hours on Tuesday. SSW flow turns increasingly W with cooling temperatures for the W slope of the Cascades as the day progresses. The situation is a bit more complex for the E slopes of the Cascades and passes where a switch from low-level E to W flow should raise freezing levels briefly during the morning hours before cooling aloft begins to lower them later in the day.
Very light snow shower activity continues Tuesday night as onshore flow arrives over a weak ridge, adding very light amounts of fresh snow above 3000 ft going into Christmas day.
A very potent system strengthens as it tracks towards southern British Columbia on Wednesday. The associated strong cold front approaches the coast late in the day, spreading increasing light, moderate, and heavy snowfall into the Cascades. Expect the heaviest snow at Mt Baker along with the strongest S winds. Low-level E flow will also increase through the mountain gaps. Most areas will see snow above 2500-3000 ft for a White Christmas!
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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Tuesday
Increasing light rain and snow showers. Moderate ridgeline winds.
Tuesday
Night
Mostly cloudy with very light snow showers at times.
Tuesday
Steadier rain and snow early transition to increasing light rain and snow showers. Weak convergence possible . Moderate ridgeline winds. Cooling trend.
Tuesday
Night
Decreasing light snow showers, locally moderate to heavy in Skagit during the evening hours if convergence materializes. Increasing moderate ridgeline winds.
Tuesday
Steadier rain and snow early transition to increasing light rain and snow showers. Weak convergence possible. Moderate ridgeline winds. Cooling trend.
Tuesday
Night
Decreasing light snow showers, locally moderate to heavy in Skagit during the evening hours if convergence materializes.
Tuesday
Steadier rain and snow early transition to light rain and snow showers. Moderate ridgeline winds. Cooling trend.
Tuesday
Night
Decreasing light rain and snow showers. Light to moderate ridgeline winds.
Tuesday
Steadier rain and snow early transition to mostly cloudy skies with light rain and snow showers. Light to moderate ridgeline winds. Light E winds switch W at the Pass.
Tuesday
Night
Decreasing light snow showers. Moderate ridgeline and light to occasionally moderate W wind at the Pass.
Tuesday
Steadier rain and snow early transition to mostly cloudy skies with light rain and snow showers. Light to moderate ridgeline winds. Light E winds switch W at the Pass.
Tuesday
Night
Decreasing light rain and snow showers. Moderate ridgeline and light to occasionally moderate W wind at the Pass.
Tuesday
Decreasing light snow showers. Rising snow levels in the morning, then lowering in the afternoon.
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).