The Pacific Northwest is off to a chilly start on Friday. A cold trough sits over the area, but with cold air at the surface, instability is limited at this point. Therefore, we expect mostly sunny skies north of I-90 for much of the day. However, a system tracking from Idaho into Montana has brought light snowfall into the southern Cascades. Along the east slopes that extends from Blewett Pass southward and from Mt Rainier southward for the west slopes. NE ridgeline winds should switch west by late morning and gradually increase as the system exits, helping switch the focus of the snowfall primarily to the southern Cascade Volcanoes by the afternoon as a very weak shortwave moves over the area. Low-density accumulations should be less than 3" in all areas.
A stronger shortwave approaches the area overnight, sliding down the back side of the trough. Light snow showers increase for the west slopes of the southern Washington Cascades and Olympics, potentially becoming moderate for the volcanoes by morning. The light to moderate snow showers spread throughout the Cascades on Saturday. Expect 2-8" of low-density snow (with up to 0.3" of water equivalent) for most areas, with the highest amounts likely for Snoqualmie Pass and Paradise. Expect light to moderate WSW winds to focus more on the southern half of the Cascades.
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
Mostly sunny to start, then filtered sunshine, with obscured skies late in the day.
Friday
Night
Cloudy with light snow developing in the early morning (moderate in the southern and eastern Olympics).
Friday
Mostly sunny with filtered sunshine in the afternoon.
Friday
Night
High clouds lower and thicken.
Friday
Mostly sunny with filtered sunshine in the afternoon (north part). Some low clouds in the morning (southern part).
Friday
Night
High clouds lower and thicken, with light snow developing in the early morning hours.
Friday
Periods of light snowfall from Mt Rainier southward. Cloudy in the morning with mostly cloudy skies in the afternoon.
Friday
Night
Increasing light snow.
Friday
Partly cloudy in the morning, then filtered sunshine in the afternoon. Light ridgeline and E winds switch W at the Pass by mid-morning.
Friday
Night
High clouds lower and thicken. Light ridge and W wind at the Pass.
Friday
Mostly cloudy in the morning, then filtered sunshine in the afternoon. Light ridgeline and E winds switch W at the Pass by mid-morning.
Friday
Night
High clouds lower and thicken. Light to occasionally moderate ridgeline and W wind at the Pass.
Friday
Mostly sunny with a frigid start. High clouds in the afternoon.
Friday
Night
High clouds lower and thicken.
Friday
Very light snow from the Wenatchee Mountains southward in the morning. Popcorn clouds in the afternoon.
Friday
Night
Increasing clouds.
Friday
Periods of very light snow through the morning hours, then mostly cloudy with a few flurries in the afternoon.
Friday
Night
Mostly cloudy with snow flurries near the Cascade Crest.
Friday
Cloudy with periods of light snow. Moderate ridgeline winds develop in the afternoon.
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).