The last act of the Christmas-Boxing day storm brings more heavy snowfall in addition to moderate to strong SSW ridgeline switching W in the mid-day hours. The low center tracks ENE from the central Puget Sound toward the mountain loop. This more southerly track has decreased the ridgeline wind forecast for the Olympics, Mt Baker, and Washington Pass areas to moderate (previously strong). A low-level shift to W winds coincides with the westerly push in the late morning hours and should raise snow levels to around 3500 ft for all areas. This won't change snow levels appreciably west of the Cascade Crest, but should result in a snow-to-rain transition for Snoqualmie Pass and low-elevation locations east of the Cascade Crest. Moisture wrapping around the low remains stratiform and steady. The back edge of this precipitation shield has reached the coast. As the package shifts eastward, we'll see a transition to a more showery regime in the Olympics by mid-day and in the Cascades during the afternoon.
Shower activity continues on W flow Thursday evening before a weaker system arrives with moderate rain and snow arriving from SW to NE. This starts overnight for Mt Hood and the Olympics, and during the morning hours on Friday for the central Washington Cascades. This system may or may not reach as far north as the North Cascades. Expect another shift from E to W winds during the mid-day hours switching pass-level precipitation at Snoqualmie from snow to rain.
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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Thursday
Moderate rain and snow becoming light rain and snow showers by the afternoon. Decreasing moderate ridgeline winds become light.
Thursday
Night
Light rain and snow showers in the evening with light rain and snow developing in the early morning hours.
Thursday
Decreasing moderate to heavy snow tapering to moderate showers late in the day. Moderate ridgeline winds at times.
Thursday
Night
Light rain and snow showers decrease and possibly end overnight.
Thursday
Decreasing moderate to heavy snow tapering to moderate showers late in the day. Convergence is likely in the southern mountain loop late in the day. Moderate ridgeline winds at times.
Thursday
Night
Light rain and snow showers decrease and possibly end overnight.
Thursday
Decreasing moderate to heavy snow tapering to moderate showers late in the day. Moderate to strong ridgeline winds peak in the late morning hours.
Thursday
Night
Light rain and snow showers with increasing light to moderate snow developing in the early morning hours.
Thursday
Decreasing moderate to heavy snow tapering to moderate showers late in the day. Moderate to occasionally strong ridgeline winds and light to moderate E winds switch W at the pass after 10 AM.
Thursday
Night
Light rain and snow showers decrease or end. Light ridgeline and W winds at the Pass switch E in the late evening hours.
Thursday
Decreasing moderate to heavy snow tapering to moderate showers late in the day. Moderate to strong ridgeline winds and moderate E winds switch W at the pass after 10 AM.
Thursday
Night
Light rain and snow showers decrease or end overnight. Light ridgeline and W winds at the Pass switch E in the late evening hours.
Thursday
Moderate snow peaks tapers to light rain and showers late in the day. Moderate to occasionally strong ridgeline winds.
Thursday
Night
Mostly cloudy with decreasing light rain and snow showers in the evening hours.
Thursday
Moderate to heavy snowfall tapers to light to moderate rain and snow showers in the afternoon. Strong ridgeline winds peak during the mid-day hours.
Thursday
Night
Mostly cloudy with decreasing light rain and snow showers in the evening hours.
Thursday
Moderate to heavy snowfall tapers to light to light rain and snow showers in the afternoon. Moderate to strong ridgeline winds peak during the mid-day hours.
Thursday
Night
Light rain and snow showers near the Cascade Crest in the evening, then light rain and snow develops overnight.
Thursday
Moderate to heavy rain and snow becomes showery late in the day. Strong ridgeline winds decrease slightly in the afternoon.
Thursday
Night
Light to moderate snow showers becomes moderate rain and snow overnight. 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).