An offshore low lifts a warm front north over the region Friday morning. The band of moderate precipitation extends from Salem, Oregon north to around Stevens Pass. Precipitation should reach the Canadian border by 11 AM. Moderate low-level E flow, combined with SE circulation with the front will create conditions for upslope snowfall on the east slopes of the Cascades and moderate ESE ridgeline winds through the mountain gaps. Behind the front, lighter snow showers continue. Winds should gradually ease as the front lifts through in the mid-morning to early afternoon hours. But don't expect a wind shift at low elevations where gradients remain weakly easterly, maintaining the precipitation type as snow at Snoqualmie Pass. Snow levels start elevated at Mt Hood, but should lower as the day progresses toward ski area bases.
Snow shower activity becomes very light as the offshore upper low and associated trough arrive. Temperatures gradually cool west of the Cascade Crest, with snow levels dropping to 2500-3000 ft for Washington State and 4000 ft for Mt Hood.
W winds increase on Saturday ahead of the next system. Light rain and snow increase in the afternoon along with ridgeline WSW winds. Once again, light E low-level winds likely maintain snow through the mountain gaps, but a mix is possible in the afternoon at Snoqualmie Pass as slightly warmer air tries to over-run it.
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 become showery in the afternoon.
Friday
Night
Light and scattered rain and snow showers.
Friday
Moderate rain and snow develop around 9 AM and continue throughout the day.
Friday
Night
Decreasing light rain and snow showers. Moderate ridgeline winds become light.
Friday
Moderate rain and snow develop around 7-9 AM and continue through mid-afternoon, then become showery.
Friday
Night
Decreasing light rain and snow showers. Moderate ridgeline winds become light.
Friday
Moderate rain and snow transition to light to moderate rain and snow showers in the afternoon. Moderate ridgeline winds.
Friday
Night
Increasing light rain and snow showers. Moderate ridgeline winds.
Friday
Light rain and snow become showery in the afternoon. Decreasing moderate ridgeline and decreasing mostly light E wind at the Pass.
Friday
Night
Light rain and snow showers. Decreasing light to occasionally moderate (WSW) ridgeline and light E wind at the Pass.
Friday
Moderate rain and snow become showery in the afternoon. Decreasing moderate ridgeline and decreasing light to moderate E wind at the Pass.
Friday
Night
Light rain and snow showers. Decreasing light to moderate (WSW) ridgeline and light E wind at the Pass.
Friday
Light snow develops by mid-morning, becoming moderate in the afternoon.
Friday
Night
Decreasing very light snow showers. Moderate ridgeline winds.
Friday
Light to moderate rain and snow becomes showery in the afternoon. Moderate ridgeline winds decrease in the afternoon.
Friday
Night
Decreasing light rain and snow showers. Moderate ridgeline winds.
Friday
Light to moderate rain and snow become light and showery by the afternoon. Moderate ridgeline winds decrease in the afternoon.
Friday
Night
Light rain and snow showers. Moderate ridgeline winds.
Friday
Moderate rain and higher elevation snow become light rain and snow showers with lowering snow levels. Increasing light to moderate ridgeline winds.
Friday
Night
Increasing light rain and snow showers. 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).