Change is afoot in the Pacific Northwest as a flattening ridge allows further cooling and opens the door to active weather. Temperatures cooled off overnight into the 30s for most mountain locations. The cooling trend should offset typical daytime warming, resulting in a more limited temperature range for many areas. The exception will be areas east of the Cascades where a strong, shallow low-level inversion set up overnight. These areas should mix out as moderate SW ridgeline winds generally stir the atmosphere. High clouds will create filtered sunshine in the morning, giving way to obscured skies in the afternoon.
A potent frontal system begins to spread precipitation into the area Thursday evening, first in the Olympics and Mt Baker areas, then spreading throughout the region overnight. By morning, expect widespread moderate to locally heavy rain and snow. Snow levels should be in the 2000-3500 ft range for the mountains of Washington, but as a warm front moves over the area Friday morning, precipitation rates become heavy. Snow levels rise by around 500-1000 ft, but E flow will likely insolate Snoqualmie Pass from the warming through at least the morning hours. The afternoon is more uncertain. The cold frontal passage should hold off until Friday evening.
Snowfall amounts should be in the 6-18" range for the Cascades through Friday above 3000 ft.
Weather Forecast
Olympics
West North
West Central
West South
Stevens Pass
Snoqualmie Pass
East North
East Central
East South
Mt. Hood
Use dropdown to select your zone
Thursday
Low clouds below 3000 ft. Above that elevation, filtered sunshine gives way to obscured skies as clouds increase.
Thursday
Night
Cloudy with light rain and snow developing overnight.
Thursday
Filtered sunshine gives way to obscured skies. Low clouds below 3000 ft.
Thursday
Night
Cloudy to start, then moderate to heavy rain and snow develop in the evening.
Thursday
Filtered sunshine gives way to obscured skies. Low clouds below 3000 ft.
Thursday
Night
Cloudy to start, then moderate rain and snow develop in the evening.
Thursday
Filtered sunshine gives way to obscured skies. Patchy low clouds below 3000 ft.
Thursday
Night
Cloudy to start, then light to moderate rain and snow develop in the evening.
Thursday
Filtered sunshine gives way to obscured skies. Patchy low clouds below 3000 ft. Light ridgeline and light W wind at the Pass.
Thursday
Night
Cloudy to start, then light rain and snow develop overnight. Mostly light ridgeline winds. Light low-level flow switches E at the Pass.
Thursday
Filtered sunshine gives way to obscured skies. Patchy low clouds below 3000 ft. Moderate ridgeline and light W wind at the Pass.
Thursday
Night
Cloudy to start, then mostly light rain and snow develop overnight. Light to moderate ridgeline winds. Light low-level flow switches E at the Pass.
Thursday
Filtered sunshine gives way to obscured skies late in the day. There is a strong low-level inversion in the morning hours. Moderate ridgeline winds at times.
Thursday
Night
Cloudy with light snow developing overnight. Light to moderate ridgeline winds.
Thursday
Filtered sunshine gives way to obscured skies late in the day. There is a strong low-level inversion in the morning hours. Moderate ridgeline winds.
Thursday
Night
Cloudy with light rain or snow developing overnight. Moderate ridgeline winds.
Thursday
Filtered sunshine gives way to obscured skies late in the day. There is a strong low-level inversion in the morning hours. Moderate ridgeline winds at times.
Thursday
Night
Cloudy with light rain or snow developing overnight. Moderate ridgeline winds.
Thursday
Filtered sunshine gives way to obscured skies. Increasing moderate ridgeline winds.
Thursday
Night
Cloudy with light rain or snow developing overnight. 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).