Atmospheric stability has increased within the post-frontal westerly flow. The result is more continuous moderate snowfall focused on the west slopes of the Cascades and Olympics through mid-morning on Friday. Westerly ridgeline winds should continue to decrease within the moderate range through the morning hours. An upper low dropping southward into the near shore water should re-orient flow gradually toward the WSW as the day progresses and to the SW by the end of the day. The result will be gradually decreasing snow for the central Cascades passes with snowfall slightly more focused on the volcanoes. The southwest slopes of the Olympics should see some moderate to heavy snow, but amounts should be light for Hurricane Ridge and the NE portion of the range.
The upper low moves into the nearshore waters by Saturday morning. Winds turn southerly aloft and E flow develops and rapidly increases overnight through the mountain gaps. Expect a significant upslope snow event with very heavy snow for the S and E Olympics, Mt. St. Helens, and perhaps Paradise late Friday night into Saturday with snow levels near sea level. Other areas should have mostly light to occasionally moderate snow or showers. However, with low-level E winds peaking in the moderate range early Saturday, 3-6" of snow remains a possibility for areas well east of the Cascade Crest such as the mountains around Leavenworth on Saturday.
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 to occasionally moderate snow showers. Moderate snow in southern Olympics.
Friday
Night
Light snow or snow showers. Heavy snow in southern and eastern Olympics.
Friday
Moderate snow becomes lighter and showery in the afternoon.
Friday
Night
Moderate snow.
Friday
Moderate snow.
Friday
Night
Moderate snow.
Friday
Moderate snow at Paradise and White Pass. Light snow at Crystal.
Friday
Night
Heavy snow at Mt. St. Helens. Moderate snow at Paradise. Light snow at Crystal and White Pass.
Friday
Light snow decreasing in the afternoon. Decreasing moderate ridgeline winds become light. Light W winds at the Pass.
Friday
Night
Decreasing light snow or snow showers. Light ridgeline winds. Light W winds shift E and become moderate by morning at the Pass.
Friday
Moderate snow decreasing in the afternoon. Decreasing moderate ridgeline winds. Moderate W winds at the Pass.
Friday
Night
Decreasing light snow or snow showers. Light ridgeline winds. Light W winds shift E and become moderate by morning at the Pass.
Friday
Light snow.
Friday
Night
Light snow.
Friday
Light snow at times.
Friday
Night
Decreasing light snow at times.
Friday
Light snow near the Cascade Crest.
Friday
Night
Light snow at times.
Friday
Moderate snow becoming light by the afternoon. 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).