A Pacific frontal system dropping south from British Columbia will spread light precipitation and increasing cloud cover southward over the course of the day. Snow levels will drop rapidly into the 3000-4000' range with the onset of precipitation. Ridgeline winds will increase during the day as well.
The main event will be tonight as the frontal boundary pushes through the Cascades between 12-2 am. After a burst of moderate precipitation, a Puget Sound convergence zone will form late tonight in the Hwy 2 and Mt Loop corridor and sag south towards I-90 into Thursday morning. This system looks like it will produce 4-12 inches of snow along the west slopes of the Cascades and Mt Hood with rapid cooling behind the front. There should be a significant spillover of snowfall downwind of the convergence zones for the east slopes near the Cascade crest. Strong W-NW winds will develop overnight and continue through the morning hours. Expect showers to taper off Thursday morning and become scattered in the afternoon. Cool cloudy conditions will persist through Thursday afternoon.
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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Wednesday
Light rain and snow developing this morning and becoming occasionally moderate in the afternoon. Increasing ridgeline winds.
Wednesday
Night
Moderate rain and snow becoming light to moderate showers after midnight. Strong ridgeline winds decreasing after midnight.
Wednesday
Light rain and snow developing this morning and becoming light to moderate in the afternoon. Strong ridgeline winds.
Wednesday
Night
Moderate rain and snow becoming moderate showers after midnight. Strong ridgeline winds decreasing after midnight.
Wednesday
Light rain and snow developing later this morning and becoming occasionally moderate in the afternoon. Increasing ridgeline winds.
Wednesday
Night
Moderate rain and snow becoming moderate showers after midnight. Strong ridgeline winds.
Wednesday
Mostly sunny in the morning, becoming cloudy late morning. Light rain and snow developing in the afternoon. Increasing ridgeline winds.
Wednesday
Night
Light to moderate rain and snow becoming light to moderate showers after midnight. Heaviest precipitation Paradise area. Strong ridgeline winds.
Wednesday
Cloudy in the morning. Light rain and snow developing late morning. Increasing ridgeline winds.
Wednesday
Night
Light to moderate rain and snow becoming moderate showers after midnight. Strong ridgeline winds.
Wednesday
Cloudy in the morning. Light rain and snow developing mid-day. Increasing ridgeline winds.
Wednesday
Night
Light to moderate rain and snow becoming moderate showers after midnight. Strong ridgeline winds.
Wednesday
Cloudy in the morning. Light rain and snow developing late morning. Increasing ridgeline winds.
Wednesday
Night
Light to occasionally moderate rain and snow becoming showers after midnight. Strong ridgeline winds decreasing after midnight.
Wednesday
Mostly cloudy in the morning. Light rain and snow developing mid-day. Increasing ridgeline winds.
Wednesday
Night
Light to occasionally moderate rain and snow becoming showers after midnight. Heaviest showers near the Cascade crest. Strong ridgeline winds.
Wednesday
Mostly sunny in the morning, becoming cloudy late morning. Light rain and snow developing in the late afternoon. Increasing ridgeline winds.
Wednesday
Night
Light to occasionally moderate rain and snow becoming light showers after midnight. Strong ridgeline winds.
Wednesday
Mostly sunny in the morning, becoming cloudy in the afternoon. Chance of light rain and snow late. Strong ridgeline winds.
Wednesday
Night
Light to moderate rain and snow becoming moderate showers late. 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).