NW flow aloft continues over the region with a ridge of high pressure offshore and a broad trough over the Great Plains to our east. This will bring a weak disturbance toward the Pacific Northwest Coastline on Thursday with increasing mid-level and high clouds across the region associated with filtered sunshine and potentially obscured skies. That disturbance moves into the Oregon Cascades during the evening hours, bringing a chance for a trace of snow to Mt Hood.
On Thursday, the atmosphere remains largely decoupled with a cold pool entrenched east of the Cascades, driving low-level E winds through mountain gaps below 5000 ft. Ridgelines generally lie above this layer and are more influenced by the light, but gradually increasing winds associated with the approaching disturbance. The bigger impact of this disturbance is to accelerate cooling aloft and to usher colder low-level air through the Fraser Gap into NW Washington late Thursday and Thursday night, then shift winds ENE along the Cascade Crest overnight. Once freezing levels drop to around 5000 ft, they effectively drop to the surface. This will occur first in areas of northern Washington and near/east of the Cascade Crest.
The clouds associated with the disturbance largely retreat by Friday morning. A ridge offshore will bring gradual warming to areas west of the Cascade Crest, but chilly conditions will continue in areas near and east of the Crest.
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
Filtered sunshine transitioning to obscured skies. Cooler.
Thursday
Night
Skies clearing in the early evening. Cooler.
Thursday
Filtered sunshine. Cooler.
Thursday
Night
Clear skies. Cooler.
Thursday
Filtered sunshine. Cooler.
Thursday
Night
Skies clearing in the early evening. Cooler.
Thursday
Filtered sunshine. Cooler.
Thursday
Night
Skies clearing in the evening. Cooler.
Thursday
Filtered sunshine. Light ridgeline winds decoupled from E winds at the Pass.
Thursday
Night
Skies clearing in the evening. Cold with temperature inversions.
Thursday
Filtered sunshine. Light ridgeline winds decoupled from moderate E winds at the Pass.
Thursday
Night
Skies clearing in the evening. Cold with temperature inversions.
Thursday
Sunshine and filtered sunshine. Strong temperature inversions.
Thursday
Night
Mostly clear. Cold with temperature inversions.
Thursday
Filtered sunshine. Strong temperature inversions.
Thursday
Night
Mid-level clouds in the evening, then clearing overnight. Cold.
Thursday
Filtered sunshine. Strong temperature inversions.
Thursday
Night
Mid-level clouds in the evening, then clearing overnight. Cold.
Thursday
Filtered sunshine transitions to obscured skies in the afternoon. Temperature inversions.
Thursday
Night
Cloudy with a chance of a trace of light snow in the evening, then partially clearing skies overnight.
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).