High pressure expanding into the region provides the Pacific Northwest with a break from an otherwise very active fall weather pattern.
Cool air continues to hold on over the Pacific Northwest Saturday night. However, the expanding high should spread warm air into mid and upper elevation locations with the warm-up occurring earlier across the Southern Cascades. A period of low-level E wind develops Saturday evening as the ridge of high pressure shifts eastward. Cooler air hanging on at low elevations east of the Cascade Crest and migrating through the Passes will create a temperature inversion as warm air rides over the top. Expect these inversions to break down during the late morning to mid-afternoon afternoon hours, resulting in a shift from below-freezing to well-above-freezing temperatures in many cases. Downslope winds should prevent inversions from forming west of the Cascade Crest and allow for much warmer conditions Saturday night into Sunday. Washington Pass may be able to avoid most of the above freezing temperatures, but most other locations below 9000 ft will not.
Sunday night will be mostly clear and mild with gradually lowering freezing levels. Low-level winds peak due to the rapid deepening of a low tracking towards the N tip of Vancouver Island as upper-level wind increases from the WSW. The associated cold front approaches with lowering clouds followed by light rain and high elevation snow to the Olympics Monday afternoon and perhaps the west slopes of the Cascades late in the day.
Use dropdown to select your zone
Mostly clear. Increasing shallow inversion with fog developing in valleys.
The cold front arrives Monday evening, bringing rapid cooling to the region along with moderate rain/snow. Snow levels should drop around 3000 ft Tuesday morning, staying below the Pass during the day as light snow shower activity continues along the west slopes of the Cascades. Snow shower activity dwindles Tuesday night. A stronger system approaches the region late Wednesday.
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).