A pair of low pressure centers located over south-central Washington and northern Oregon are quickly moving east. With it, a band of heavy stratiform precipitation shifted east of Mt Hood. A band of moderate to locally heavy rain and snow will linger over the central Washington Cascades and could bring 3-6" snow to Snoqualmie Pass, Salmon La Sac, Blewett Pass, and Mission Ridge before it exits eastward.
The next low tracks toward British Columbia. Hot on the heels of the departing system, the next round arrives in the afternoon hours. Precipitation will spread into the region from the southwest, particularly for the west slopes of the southern and central Cascades. This rain and snow could be moderate by the end of the day. Moderate rain and snow impacts the region overnight ahead of a frontal passage on Saturday morning with moderate to locally heavy rain and snow and a slight increase in snow levels from around 2500-3000 ft Friday and Friday night to 3000-4000 ft on Saturday. Snoqualmie Pass likely experiences snow levels jumping above the Pass with an E to W low-level wind shift.
The west slopes of the Cascades above the rain-snow line can expect 6-20" over the period, with the highest amounts at Paradise, Mt Hoodm Mt Baker, and Washington Pass.
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
Light rain and snow (moderate southern part) end during the morning g hours. Light rain and snow re-develop for the SW Olympics in the afternoon.
Friday
Night
Light to occasionally moderate rain and snow. Moderate ridgeline winds.
Friday
Mostly cloudy. Light rain and snow develop late in the day.
Friday
Night
Heavy rain and snow. Moderate to occasionally strong ridgeline winds.
Friday
Light rain and snow in the morning (mainly south of the mountain loop). Then light rain and snow spreads across the area late in the day.
Friday
Night
Moderate to occasionally heavy rain and snow. Moderate ridgeline winds.
Friday
Periods of light to occasionally moderate rain and snow, heaviest in the afternoon.
Friday
Night
Increasing moderate to heavy rain and snow at Paradise (light to moderate at Crystal and White Pass). Increasing moderate ridgeline winds.
Friday
Periods of light rain and snow, mainly in the morning hours. Light ridgeline and E wind at the Pass.
Friday
Night
Increasing moderate rain and snow. Increasing light to moderate ridgeline and E wind at the Pass.
Friday
Periods of moderate rain and snow. Light ridgeline and E wind at the Pass. Snow level slightly below the pass.
Friday
Night
Increasing moderate to possibly heavy rain and snow. Moderate ridgeline and light to moderate E wind at the Pass.
Friday
Periods of light snow in the morning, then mostly cloudy skies.
Friday
Night
Increasing light to moderate rain and snow.
Friday
Periods of light to occasionally moderate rain and snow, decreasing in the afternoon. Moderate ridgeline winds develop in the afternoon.
Friday
Night
Increasing light to moderate rain and snow. Increasing moderate ridgeline winds.
Friday
Periods of light to occasionally moderate rain and snow, decreasing in the afternoon. Moderate ridgeline winds develop in the afternoon.
Friday
Night
Increasing light to occasionally moderate rain and snow. Increasing moderate ridgeline winds.
Friday
Light rain and snow at times, becoming moderate late in the day. Moderate ridgeline winds.
Friday
Night
Moderate rain and snow. Moderate ridgeline winds become strong overnight.
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).