A strong ridge of high pressure dominates our weather this week in the Pacific Northwest. A trough exited to the east of our region Thursday night, leaving dry NNW flow aloft as the high pressure centered off the coast of California expends into our region on Friday. The sinking motion under the high leaves our mountains with increasingly sunny weather as low clouds banked against the west slopes of the Cascades by W low-level flow gradually dissipate. Many areas start the day chilly on Friday morning, but increasingly the sinking, warming air under the high will displace the colder temperatures in place. The shift to above freezing temperatures has already occurred more rapidly at Hurricane Ridge with temperatures rising above freezing as freezing levels on the coast at Quillayute rose to 9000 ft early Friday morning. Inversions have formed in parts of the southern Washington Cascades and Mt. Hood areas as the sun will be needed to mix the cool air at lower elevations. By the afternoon, freezing levels should rise to 5000-9000 ft across the region.
Friday night, the static weather pattern will produce stronger inversions and more extensive lowland fog (below 2000 ft). Temperatures will likely hover near or above freezing for many of our mountain locations, with lower elevations dropping into the 20s. Skies should remain clear to help the radiational cooling.
Saturday should be the warmest day of this high-pressure ridge at many mountain locations. Sunny weather will help quickly revert the inversion during the morning hours. Many mountain locations will see temperatures soar into the 40s. Freezing levels should rise to 10,500 to 11,500 ft by the afternoon.
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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Friday
Mostly sunny with thin high clouds. Valley fog possible early in the morning.
Friday
Night
Clear skies with an inversion and valley fog developing.
Friday
Partly cloudy with a mix of low and thin high clouds. Valley fog possible early.
Friday
Night
Clear skies with an inversion and valley fog developing.
Friday
Partly cloudy with a mix of low and thin high clouds. Valley fog possible early.
Friday
Night
Clear skies with an inversion and valley fog developing.
Friday
Mostly sunny. Valley fog possible early.
Friday
Night
Clear skies with an inversion and valley fog developing.
Friday
Partly cloudy. Light W wind at the Pass.
Friday
Night
Mostly clear. Light W wind at the Pass, possibly switching E in the early morning hours.
Friday
Partly cloudy. Light W wind at the Pass.
Friday
Night
Mostly clear with an inversion forming. Light W wind at the Pass, possibly switching E in the early morning hours.
Friday
Mostly sunny with low clouds dissipating and filtered sunshine. Valley fog possible in deeper valleys.
Friday
Night
Mostly clear. Inversion and low elevation fog possible.
Friday
Filtered sunshine. Valley fog possible in deeper valleys.
Friday
Night
Mostly clear. Inversion and low elevation fog possible.
Friday
Mostly sunny with low clouds dissipating and filtered sunshine. Inversion mixing out around mid-morning.
Friday
Night
Mostly clear. Inversion and low elevation fog forming.
Friday
Mostly sunny. Valley fog possible in deeper valleys.
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).