We have cyclonic flow over the area with the polar vortex carving out a trough and cool NW flow over the area. A weak upper level disturbance dropping SE in the flow should help enhance precipitation this afternoon. This will be good for snow production, especially for the central Cascades.
Stevens and Snoqualmie Passes and the Mountain Loop Hwy should see an additional 6-15 inches of snow today. Shower activity should be more scattered elsewhere with lighter snowfall accumulations. Winds will be the other main story, with strong West ridgeline winds in most areas continuing through this evening. Alpine winds will push into the extreme category for the south Washington Cascades and Mt Hood during this period.
A convergence zone is likely to form later this afternoon and evening. Mesoscale models have it continuing to focus on Snoqualmie Pass but as always, convergence zones can be tricky to pin down. Showers and winds should decrease later tonight and further into tomorrow. We'll start to see low level flow become more northerly through the Fraser Valley and easterly on the east-side of the Cascades tomorrow. Light snow showers and clouds should be the general rule of thumb with some of the coldest air of the season in place over the PNW.
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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Sunday
Mostly cloudy with scattered light to occasionally moderate snow showers.
Sunday
Night
Mostly cloudy with light scattered snow showers decreasing after midnight.
Sunday
Cloudy with scattered light to occasionally moderate snow showers.
Sunday
Night
Mostly cloudy with light scattered snow showers decreasing after midnight.
Sunday
Cloudy with light to moderate snow showers. Strong ridgeline winds.
Sunday
Night
Cloudy with light to moderate snow showers in the evening becoming scattered showers after midnight. Strong ridgeline winds decreasing after midnight.
Sunday
Cloudy with light to occasionally moderate snow showers. Showers heaviest Paradise and White Pass areas. Strong ridgeline winds approaching extreme in the alpine.
Sunday
Night
Mostly cloudy with light scattered snow showers decreasing after midnight. Strong ridgeline level winds decreasing after midnight.
Sunday
Cloudy with light to moderate snow showers. Strong ridgeline and Pass level winds.
Sunday
Night
Cloudy with light to moderate snow showers in the evening becoming scattered showers after midnight. Strong ridgeline and Pass level winds decreasing after midnight.
Sunday
Moderate to occasionally heavy snow showers. Strong ridgeline and Pass level winds.
Sunday
Night
Cloudy with moderate snow showers in the evening becoming scattered showers after midnight. Strong ridgeline and Pass level winds decreasing after midnight.
Sunday
Cloudy with scattered light snow showers.
Sunday
Night
Mostly cloudy with scattered light to occasionally moderate snow showers.
Sunday
Mostly cloudy with scattered light snow showers. Strong ridgeline winds.
Sunday
Night
Mostly cloudy with scattered light to occasionally moderate snow showers. Strong ridgeline winds decreasing after midnight.
Sunday
Mostly cloudy with scattered light snow showers. Strong ridgeline winds.
Sunday
Night
Partly to mostly cloudy with isolated snow showers. Strong ridgeline winds decreasing after midnight.
Sunday
Mostly cloudy with scattered light to occasionally moderate snow showers. Showers heaviest west side, more sunbreaks Meadows area. Strong ridgeline winds approaching extreme in the alpine.
Sunday
Night
Mostly cloudy with scattered light snow showers. Strong 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).