A weak high pressure maintains mostly sunny skies Wednesday morning. Temperatures have started mild west of the Cascade Crest with diminishing downslope E winds. Somewhat cooler temperatures can be found E of the Cascade Crest. As the upper-level high shifts east late in the day a subtle shortwave trough approaches the coastline with a chance for scattered rain/snow showers for the Olympics, Mt Hood, and possibly the Mt. Rainier area late in the day. Light rain/snow showers expand northward to most areas south of I-90 during the evening area and spread throughout the region overnight as W winds gradually increase and shift gradually toward the SW ahead of an approaching cold low dropping south from the Gulf of Alaska.
The approaching cold low will be accompanied by a frontal passage during the mid-day hours on Thursday. Expect moderate SW winds and precipitation ahead of the front with a switch to W winds that may become locally strong through the mountain gaps and E of the Cascades late in the day. Snow levels lower Wednesday night down to around Snoqualmie Pass level or slightly below, with further cooling behind the front late in the day. With colder temperatures, conditions become favorable for significant snow accumulation 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
Mostly sunny in the morning, transitioning to mostly cloudy with a chance of light rain/snow showers late in the day.
Wednesday
Night
Isolated light rain/snow showers.
Wednesday
Mild. Mostly sunny with filtered sunshine at times.
Wednesday
Night
Increasing clouds with light rain/snow showers overnight.
Wednesday
Mild. Mostly sunny with filtered sunshine at times.
Wednesday
Night
Increasing clouds with light rain/snow showers overnight.
Wednesday
Mild. Mostly sunny in the morning, then becoming partly cloudy with a chance of scattered rain/snow showers late in the day.
Wednesday
Night
Mostly cloudy with light rain/snow showers.
Wednesday
Mostly sunny and mild. Light ridgeline and light E switching W winds at the Pass.
Wednesday
Night
Mostly clear to start, then becoming mostly cloudy with light rain/snow showers. Increasing light ridgeline and light W winds at the Pass.
Wednesday
Mostly sunny and mild. Light ridgeline and light E switching W winds at the Pass.
Wednesday
Night
Mostly clear to start, then becoming mostly cloudy with light rain/snow showers. Increasing light ridgeline and light W winds at the Pass.
Wednesday
Mostly sunny with filtered sunshine.
Wednesday
Night
Mostly clear with a chance of rain/snow showers in the early morning hours.
Wednesday
Mostly sunny with filtered sunshine.
Wednesday
Night
Increasing clouds with a chance of rain/snow showers.
Wednesday
Mostly sunny in the morning with increasing clouds in the afternoon.
Wednesday
Night
Increasing light rain/snow showers.
Wednesday
Mostly sunny with increasing clouds in the afternoon and a light rain/snow showers developing late in the day.
Wednesday
Night
Light to occasionally moderate rain/snow showers. Increasing 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).