The frontal boundary that dragged SE across the region on Sunday remains with to start the work week. A relatively narrow band of mostly moderate precipitation band lies between Seattle and Portland with a SSW-NNE orientation. Significantly cooler mountain temperatures (in the 20s) have worked their way into the Olympics and Mt Baker areas. South and East of the frontal boundary, temperatures are very mild with freezing levels around 9000 ft for Mt Hood. A range of snow levels exists across the frontal band. A significant wave formed just off the Oregon/California coast and should continue to expand the precipitation shield as the wave moves toward northern Oregon. Snow levels should hold relatively steady across the region as precipitation continues to focus on the central and southern Washington Cascades with lighter precipitation extending northward. Mt Hood remains in the warm sector of the storm with intermittent precipitation much of the day and steadier precipitation redeveloping as a deep upper trough kicks the frontal boundary eastward Monday night.
Temperatures cool with the incoming deep upper trough and precipitation turns significantly lighter and more showery Monday night, focusing on the west slopes of the Cascades. Moderate to strong ridgeline winds peak for Mt Hood as winds shift WSW. However, most areas of Washington state remain with light to occasionally moderate ridgeline winds. Snow levels should drop to around 2000-3000 ft by early Tuesday.
Light snow showers continue to focus on the W slopes of the Cascades with the trough squarely over the region. Expect intense, convective showers to peak in the afternoon with the colder air overhead and spring sunshine heating the surface. The west slopes of the Cascades can expect 2-6" of snow during the day with an inch or so of spillover for the east slopes.Snow levels remain near or below 3000 ft.
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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Monday
Cloudy with periods of light rain and snow (more continues in SE Olympics).
Monday
Night
Light rain and snow showers.
Monday
Light rain and snow.
Monday
Night
Light rain and snow becoming showery by morning.
Monday
Light to moderate rain and snow.
Monday
Night
Light rain and snow becoming showery by morning.
Monday
Moderate rain and high-elevation snow (heavy at times on the Volcanoes).
Monday
Night
Decreasing light rain and snow becoming showery.
Monday
Light to moderate rain and snow. Light ridgeline and W wind at the Pass.
Monday
Night
Decreasing light rain and snow showers. Light to occasionally moderate ridgeline and W wind at the Pass.
Monday
Moderate rain and snow. Light ridgeline and W wind at the Pass.
Monday
Night
Decreasing light rain and snow showers. Snow level dropping back down to the Pass level in the early morning hours. Light to occasionally moderate ridgeline and W wind at the Pass.
Monday
Light rain and snow.
Monday
Night
Decreasing light rain and snow showers.
Monday
Light to moderate rain and high-elevation snow.
Monday
Night
Decreasing light rain and snow showers.
Monday
Light to moderate rain and high-elevation snow.
Monday
Night
Decreasing light rain and snow showers.
Monday
Moderate rain and high-elevation snow. Moderate to strong ridgeline winds.
Monday
Night
Decreasing light to moderate rain and snow showers. 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).