Cold weather continues into the weekend . The PNW remains influenced by a low passing to our east and a relatively stationary closed low off the central British Columbia Coastline. The resulting W and WSW flow will maintain mostly light snow shower activity Friday night, but some convergence focused between Stevens Pass and the Mountain loop will produce locally moderate snow totals through the evening hours. A weak ridge builds on Saturday as the flow shifts SSWerly ahead of a slow-moving upper low. Scattered snow showers focus on Mt Baker (in the morning) and the southern Olympics (in the afternoon). Expect isolated snow showers by the afternoon with snow levels rising to 2500 ft. Skies should partially clear in many areas. Lingering snow showers taper off Saturday evening, allowing for significant clearing overnight and valley fog formation east of the Cascades. On Sunday, a disturbance tracks toward the Washington coastline on SW flow, ushering in the change to active weather. Light snowfall increases from S to N as the day progresses with snowfall becoming moderate at Mt Hood late in the day. SW winds ramp up into the moderate range in some areas during the afternoon as snow levels approach 3000 ft in many areas by the afternoon. Increasing low-level E flow should keep the passes slightly cooler.
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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Friday
Night
Very light snow showers.
Saturday
Increasing light snow showers.
Friday
Night
Increasing light snow showers.
Saturday
Decreasing light snow showers.
Friday
Night
Light snow showers may be moderate at times in convergence.
Saturday
Decreasing light snow showers.
Friday
Night
Light snow showers.
Saturday
Decreasing light snow showers.
Friday
Night
Light snow showers (moderate in convergence). Light to moderate ridgeline and light W winds at the Pass.
Saturday
Decreasing light snow showers. Light ridgeline and W wind at the Pass.
Friday
Night
Light snow showers. Moderate ridgeline and light to moderate W winds at the Pass.
Saturday
Decreasing light snow showers. Light ridgeline and W wind at the Pass.
Friday
Night
Light snow showers.
Saturday
Light snow showers with mostly cloudy skies.
Friday
Night
Light snow showers.
Saturday
Light snow showers with mostly cloudy skies.
Friday
Night
Light snow showers with partial clearing.
Saturday
Light snow showers with partial clearing.
Friday
Night
Decreasing light to occasionally moderate snow showers. Moderate ridgeline winds.
On Sunday night, the developing low tracks into western Washington on SW flow, spreading moderate to heavy rain and snow throughout the mountain regions. Snow levels rise to 3000-3500 ft, but will be slower to rise through the mountain gaps with moderate E low-level flow. The guiding offshore upper trough drifts toward the coast waters, gradually easing the moisture feed from NW to SE on Monday. Moderate snow showers and locally heavy convergence focus on the west slopes of the Cascades during the evening and become mostly light overnight. On Tuesday, another developing low off the Oregon Coast may start spreading a new wave of moisture into our region.
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).