A trough extends from the Gulf of Alaska into our offshore waters with a surface low tracking northward toward British Columbia out ahead of it. This has set up a prolonged period of SSW flow and the first warm system our region has experienced in some time. A shield of light to moderate precipitation will become locally heavy for Mt St Helens and Mt Baker by the afternoon as snow levels rise to around 5000-6000 ft. Rain and snow peak as a front approaches Thursday evening with moderate to occasionally strong SSW winds and moderate to locally heavy precipitation targeting the volcanoes. Most other areas can expect light to moderate rain and high-elevation snow, with the flow pattern producing mostly light precipitation for the mountain gaps. Rain, snow, and winds ease slightly overnight, with little in the way of a wind shift.
Rain and snow turns mostly light and showery on Friday with snow levels dropping to around 4500 ft. Winds turn to the SW with an approaching and flattening trough.
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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Thursday
Increasing light rain and snow (moderate to heavy southern and eastern Olympics). Moderate ridgeline winds.
Thursday
Night
Light to moderate rain and snow peaking during the evening hours (moderate to heavy in the southern and eastern Olympics).
Thursday
Moderate rain and snow becoming heavy from late morning onward. Moderate ridgeline winds.
Thursday
Night
Heavy rain and snow peaks in the evening hours. Moderate to strong ridgeline winds.
Thursday
Increasing light rain and snow.
Thursday
Night
Moderate rain and snow.
Thursday
Moderate rain and snow (heavy at Mt. St Helens and mostly light at White Pass).
Thursday
Night
Moderate rain and snow (heavy at Mt. St Helens and mostly light at White Pass).
Thursday
Light rain and snow at times. Increasing light to moderate ridgeline and E wind at the Pass.
Thursday
Night
Decreasing light rain and snow. Decreasing light to moderate ridgeline and E wind at the Pass.
Thursday
Light rain and snow at times. Increasing light to moderate ridgeline and E wind at the Pass.
Thursday
Night
Decreasing light rain and snow. Decreasing light to moderate ridgeline and E wind at the Pass.
Thursday
Increasing light rain and snow.
Thursday
Night
Light rain and snow.
Thursday
Increasing light rain and snow (may become moderate in the mountains near Leavenworth).
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).