A closed upper low spins in the offshore waters west of Vancouver Island early Wednesday. A broad shield of clouds parallels the coastline in association with a front that advances ahead of the upper low. This front will bring periods of increasing light-to-moderate precipitation to the region on Wednesday. Although snow levels start the day at around 3000 ft, expect a rise to around 4000 ft as the front reaches the Cascades in the afternoon. SSW ridgeline winds can be found in advance of the front, but low-level E flow peaking late morning will skew the wind direction SEerly for the mountain gaps and areas near the Crest, where the winds are likely to be most impactful.
The frontal system lifts northward through Thursday evening and lingers over the northern Cascades until around midnight, bringing some additional light-to-moderate, steady precipitation to these areas. Shower activity and cooling fill in behind the frontal system, with snow levels lowering to around 2000 ft by Thursday morning. Light to occasionally moderate snow showers continue for the west slopes of the Cascades on Thursday, gradually tapering in the afternoon. Expect more sunshine and milder temperatures further east.
Weather Forecast
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Snoqualmie Pass
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East South
Mt. Hood
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Wednesday
Increasing periods of light to moderate rain and snow.
Wednesday
Night
Light to moderate rain and snow early becoming light and showery.
Wednesday
Moderate rain and snow. Moderate ridgeline winds in the morning.
Wednesday
Night
Moderate rain and snow in the evening with light rain and snow showers overnight.
Wednesday
Increasing light to moderate rain and snow.
Wednesday
Night
Moderate rain and snow becoming showery overnight.
Wednesday
Increasing moderate to locally heavy rain and snow.
Wednesday
Night
Decreasing light to moderate rain and snow showers. Moderate ridgeline winds near the Cascade Crest.
Wednesday
Periods of light rain and snow. Increasing light ridgeline and E wind at the Pass.
Wednesday
Night
Mostly light rain and snow showers. Light to moderate ridgeline and light W wind at the Pass.
Wednesday
Periods of light rain and snow. Increasing light to moderate ridgeline. Light to moderate E wind at the Pass peaks in the late-morning hours.
Wednesday
Night
Mostly light rain and snow showers. Moderate ridgeline and light to moderate W wind at the Pass.
Wednesday
Periods of light rain and snow.
Wednesday
Night
Light snow becomes showery in the early morning hours.
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).