The ridge of high pressure dominating our January weather pattern is on its last legs. Wednesday morning has the telltale signs of a strong ridge with strong inversions east of the Cascade Crest and in the mountain gaps. In the 3500-4000 ft range, these inversions are impressive with temperatures rising 20F with a mere 750 ft of elevation gain in places like Snoqualmie Pass. As the offshore ridge gradually flattens, expect light to moderate W and WNW ridgeline winds to impact the Cascades' mountain gaps and E slopes. It will also mix out the low-level inversions in areas south of the Methow.
The first signs of significant change arrive overnight as high clouds spread across the region and freezing levels drop significantly over NW Washington. The flattened ridge reaches the coast on Thursday as WSW and SW ridgeline winds increase. High clouds lower and thicken, with a chance of very light rain or snow for the west slopes of the Olympics late in the day. Freezing levels continue to lower across the mountains of Washington but will be slower to arrive in the southern and eastern Cascades.
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
Sunny and mild.
Wednesday
Night
Clear with high clouds increasing.
Wednesday
Sunny and mild.
Wednesday
Night
Clear with high clouds increasing.
Wednesday
Sunny and mild.
Wednesday
Night
Clear with high clouds increasing.
Wednesday
Sunny and mild.
Wednesday
Night
Clear with high clouds increasing and mild.
Wednesday
Sunny and mild above around 4000 ft, cold to start below that elevation, then moderating. Light to occasionally moderate ridgeline and variable switching W wind at the Pass.
Wednesday
Night
Clear with high clouds increasing. Weaker inversions form overnight. Light ridgeline and W wind at the Pass.
Wednesday
Sunny and mild above 3500-4000 ft, cold to start below that elevation, then moderating. Light to occasionally moderate ridgeline and variable switching W wind at the Pass.
Wednesday
Night
Clear with high clouds increasing. Weaker inversions form overnight. Light to occasionally moderate ridgeline and light W wind at the Pass.
Wednesday
Sunny and mild above 5500-6000 ft, cold below. Light to moderate ridgeline winds.
Wednesday
Night
Clear with high clouds increasing. Weaker inversions form overnight. Light to occasionally moderate ridgeline winds.
Wednesday
Sunny and mild above 4000 ft. Cold to start below that elevation, but moderating. Light to moderate ridgeline winds.
Wednesday
Night
Clear with high clouds increasing and mild. Weaker inversions form overnight. Light to occasionally moderate ridgeline winds.
Wednesday
Sunny and mild above 4000 ft. Cold to start below that elevation, but moderating. Light to moderate ridgeline winds.
Wednesday
Night
Clear with high clouds increasing and mild. Weaker inversions form overnight. Light to occasionally moderate ridgeline winds.
Wednesday
Sunny and mild above 4000 ft. Cold to start below that elevation, but moderating. Light to occasionally moderate ridgeline winds.
Wednesday
Night
Clear with high clouds increasing and mild. Weaker inversions form overnight. Light to occasionally 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).