An upper-level trough shifts east of the region with showers spilling over the top of a flattened ridge offshore. South of I-90 these showers are arriving on W winds and should gradually decrease during the day. North of I-90 shower activity should increase slightly as the day progresses with WSW winds turning SWerly as a stronger frontal system approaches the region from the NW. Snow levels should rise from below 3000 ft to just above 3000 ft by the afternoon. Near and east of the Cascade Crest, some areas such as Crystal Mountain, White Pass, and Mt. Hood should continue to experience moderate to strong ridgeline winds.
A moisture-laden front approaches our region Monday night with increasing moderate to heavy rain and snow for the western Olympics and Mt. Baker with increasing light to moderate moderate rain/snow for other areas of Washington. A warm sector of the storm should allow snow levels to rise to around 4500 ft for the Olympics and 3500 ft for most other areas.
A cold front moves through from WNW to ESE on Tuesday in the early afternoon with heavy rain and snow across the region and strong post-frontal W flow maintaining the precipitation. Mt. Baker stands to receive the most snowfall (18-24") Monday night with other areas of the Cascades west slopes above 4000 ft expected to pick up 6-18" over the same time frame.
Updated 7:20 AM to specify the timing of the approaching front on Monday night.
Light rain and snow showers. Increasing moderate ridgeline winds.
Monday
Night
Moderate rain and snow becoming heavy. Moderate to strong ridgeline winds.
Monday
Light rain and snow showers.
Monday
Night
Light rain and snow becoming moderate. Moderate to occasionally strong ridgeline winds.
Monday
Generally light rain and snow showers (heaviest at Paradise) with shower activity decreasing in the afternoon. Moderate to occasionally strong ridgeline winds.
Monday
Night
Increasing light rain and snow (heaviest at Paradise).
Monday
Light rain and showers. Increasing moderate ridgeline and light to occasionally moderate W winds at the Pass.
Monday
Night
Increasing light rain and snow. Moderate ridgeline and light W wind at the Pass.
Monday
Light rain and showers. Increasing moderate ridgeline and light to occasionally moderate W winds at the Pass.
Monday
Night
Increasing light rain and snow. Moderate ridgeline and light W wind at the Pass.
Monday
Increasing light rain and snow showers. Moderate ridgeline winds with strong gusts.
Monday
Night
Increasing light to occasionally moderate rain and snow. Moderate ridgeline winds with strong gusts.
Monday
Increasing light rain and snow showers. Moderate ridgeline winds with strong gusts.
Monday
Night
Increasing light rain and snow. Moderate to strong ridgeline winds with strong gusts.
Monday
Very light rain or snow showers at times. Moderate ridgeline winds with strong gusts.
Monday
Night
Mostly dry in the evening with a chance of rain or snow overnight. Moderate ridgeline winds with strong gusts.
Monday
Light rain or snow showers, mainly in the morning hours. Decreasing moderate to strong ridgeline winds.
Monday
Night
Cloudy. Increasing moderate to 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).