A moisture-laden frontal system moves over the region on Sunday as an offshore trough rotates NE into Canada. Snow levels will oscillate in the 4000-5000 ft range with the potential for E flow to drag snow levels locally lower in the passes during the morning hours or create spotty freezing rain. Precipitation will be moderate in intensity early in the day, with greater emphasis on the volcanoes, then light to moderate, increasingly showery, and more focused on the passes as moderate ridgeline winds shift from SSW to WSW by the afternoon, and snow levels will be slightly lower.
Mostly light rain and snow showers gradually decrease with only a subtle drop in snow levels during the evening hours. Attention shifts to Skagit and Whatcom counties during this time as a locally heavy band of convergence brings higher precipitation rates to the Mt Baker area. It's not exactly certain where this will set up.
While southern areas get a brief break in the action through early Monday, the next frontal system spreads, increasing mostly light rain and snow into the central Washington Cascades early in the day. Light to moderate rain and snow expand into the southern Washington Cascades and intensify slightly in the afternoon. Snow levels rise from around 3000-4000 ft in the morning up to 3500-5000 ft in the afternoon, with some uncertainty in the degree of warming as the moisture moves over an expanding ridge.
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
Light rain and snow (moderate in the southern Olympics) become lighter and showery by late morning. Decreasing light to moderate ridgeline winds.
Sunday
Night
Occasional light rain and snow showers.
Sunday
Moderate to heavy rain and snow decreases in the afternoon. Moderate to strong ridgeline winds become light to moderate by mid-morning.
Sunday
Night
Moderate to heavy convergence bands in the evening, otherwise decreasing light rain and snow showers.
Sunday
Moderate rain and snow decrease and become showery in the afternoon. Increasing light to moderate ridgeline winds.
Sunday
Night
Decreasing light rain and snow showers.
Sunday
Moderate rain and snow decrease and become showery in the afternoon. Increasing light to moderate ridgeline winds.
Sunday
Night
Decreasing light rain and snow showers.
Sunday
Periods of moderate rain and snow. Snow levels start at the Pass, but may rise in the afternoon. Increasing light to moderate ridgeline winds. Light E wind at the Pass shifts W by 10 AM.
Sunday
Night
Decreasing light rain and snow showers. Light to moderate ridgeline and light W wind at the Pass.
Sunday
Moderate rain and snow, with a chance of patchy freezing rain early. Increasing light to moderate ridgeline winds. Light to moderate E wind at the Pass shifts W by 10 AM.
Sunday
Night
Decreasing light rain and snow showers. Light to moderate ridgeline and mostly light W wind at the Pass.
Sunday
Increasing mostly light rain and snow. Increasing light to 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).