High pressure remains in place over the region. Most ridgelines experienced light easterly winds overnight with high thin clouds passing over the majority of western Washington. The thickest cloud cover is focused near Mount Hood. Dense fog has developed on the west side of the Cascades, while low-level clouds persist east of the Crest, particularly near Snoqualmie Pass.
A strong temperature inversion is entrenched across the forecast area, trapping cold air in low-lying terrain, generally below 5,000 to 6,000 feet. Above the inversion, northwest winds have taken hold. The dominant wind direction at ridgeline will depend on the elevation of the inversion layer: easterly winds are likely below the inversion, while northwest winds can be expected above it.
A weak system will move in from the northwest Wednesday night into Thursday. Impacts will be minimal, aside from a modest increase in cloud cover. Overall, cloud coverage should remain similar to Tuesday and Wednesday, mostly thin and low impact. Easterly flow will continue through the mountain gaps, lightening overnight Wednesday, and strengthening Thursday afternoon. Freezing levels will continue to lower.
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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Wednesday
High clouds, and mild. Temperature inversion, with cold air trapped in low-lying areas. Cooling temperatures through the day.
Wednesday
Night
High clouds. Cooling temperatures overnight.
Wednesday
High clouds, and mild. Temperature inversion, with cold air trapped in low-lying areas. Cooling temperatures through the day.
Wednesday
Night
High clouds. Cooling temperatures overnight.
Wednesday
High thin clouds. Temperature inversion, with cold air trapped in low-lying areas. Cooling temperatures through the day.
Wednesday
Night
High thin clouds. Cooling temperatures overnight.
Wednesday
High thin clouds. Temperature inversion, with cold air trapped in low-lying areas. Light to moderate ridgeline wind.
Wednesday
Night
High thin clouds. Cooling temperatures overnight.
Wednesday
Strong temperature inversion, trapping colder air below 6,000 feet. Light to moderate ridgeline and E wind at the Pass.
Wednesday
Night
High thin clouds. Cooling temperatures. Light to moderate ridgeline and E wind at the Pass.
Wednesday
Fog west of the Crest, and low clouds east of the Crest. Temperature inversion, trapping colder air below 6,000 feet. Moderate ridgeline and E wind at the Pass.
Wednesday
Night
High thin clouds. Cooling temperatures. Light to moderate ridgeline and E wind at the Pass.
Wednesday
High clouds. Strong temperature inversion, trapping colder air below 6,000 feet.
Wednesday
Night
High clouds. Cooling temperatures overnight.
Wednesday
Low level clouds against the Crest. High clouds away from the Crest. Strong temperature inversion, trapping colder air below 6,000 feet.
Wednesday
Night
High clouds. Cooling temperatures overnight.
Wednesday
High thin clouds. Temperature inversion, with cold air trapped below 5000 feet.
Wednesday
Night
High thin clouds. Cooling temperatures overnight.
Wednesday
High thin clouds. Temperature inversion, with cold air trapped below 5000 feet. Moderate 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).