A weak frontal system moving into our nearshore waters on Sunday keeps intense instability showers focused on the Olympics and Mt Baker areas on Sunday morning. Expect moderate to locally heavy snow to increase in these areas as the day progresses. Other areas will remain mostly cloudy with more isolated shower activity through the morning. As this feature moves towards the coast, shower activity moves back into the rest of the Cascades at some point during the afternoon hours. Moderate snow showers peak for these areas with the frontal passage Sunday evening, while elevated chances for convergence maintain heavy snowfall in parts of the West North Cascades. Snow shower activity tapers overnight as winds shift from SSW to WSW, and low-level winds through the Cascade Passes shift W.
Monday should be nearly a carbon copy of Sunday with another system approaching the coastline. Heavier precipitation once again targets the Olympics and Mt Baker areas on SSW flow, with E flow returning through the mountain gaps.
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
Moderate to occasionally heavy snow showers. Moderate ridgeline winds by the afternoon.
Sunday
Night
Decreasing light snow showers. Moderate ridgeline winds in the evening.
Sunday
Increasing heavy snow. Increasing moderate ridgeline winds.
Sunday
Night
Decreasing moderate to heavy snow showers and strong convergence banding. Decreasing light to moderate ridgeline winds.
Sunday
Increasing light snow showers. Increasing light to moderate ridgeline winds.
Sunday
Night
Decreasing moderate snow showers. Increasing light to moderate ridgeline winds.
Sunday
Cloudy with increasing chances for rain and snow showers from late morning onwards.
Sunday
Night
Decreasing moderate snow showers. Increasing light to moderate ridgeline winds.
Sunday
Cloudy with increasing chances for light snow showers from late morning onwards. Light ridgeline and E wind at the Pass.
Sunday
Night
Decreasing light snow showers. Increasing light to moderate ridgeline winds. Light E winds shift W at the Pass.
Sunday
Cloudy with increasing chances for light rain and snow showers from late morning onwards. Light ridgeline and E wind at the Pass.
Sunday
Night
Decreasing moderate snow showers. Increasing light to moderate ridgeline winds. Light E winds shift W at the Pass.
Sunday
Occasional light snow showers.
Sunday
Night
Mostly light snow showers. Increasing light to moderate ridgeline winds.
Sunday
Mostly cloudy in the morning with a few rain or snow showers in the afternoon.
Sunday
Night
Light snow showers. Light to moderate ridgeline winds.
Sunday
Mostly cloudy.
Sunday
Night
Light snow showers. Light to moderate ridgeline winds.
Sunday
Mostly cloudy with light snow showers late in the day.
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).