A ridge over the West Coast shifts east on Thursday as a warm front brings a light band of steadier precipitation to NW Washington. That band is bringing rain rates up to 0.15" per hour over the 542 corridor west around Mt Baker as it lifts north into Canada. Expect mild air to continue flowing into the region on a SSW flow with light showers continuing for the Olympics and portions of the west slopes of the Cascades through the afternoon.
The ridge aloft has created inversion conditions east of the Cascades with a cold pool thickening as the day progresses and E low-level flow increases in the light to moderate range. This could create a wintry mix for any precipitation spilling over into the passes.
A modest trailing cold frontal precipitation band will impact the mountains of Washington State during the evening hours. In most areas, precipitation will be light, but Moderate to occasionally strong SSW winds peak around Mt Baker and will help squeeze out a period of heavy rainfall before precipitation rapidly tapers overnight. Washington Pass could pick up 1-6" of snowfall during this time frame, with upslope snowfall potentially bringing accumulations to lower elevations. Precipitation further south is more likely to be mixed as warm air spreads in aloft.
Shortwave ridging brings the region a mostly dry morning on Friday. Temperatures remain unseasonably mild with freezing levels around 10,000 ft for the Olympics, Mt Hood, and the southern Washington Cascades. Light rain and highest elevation snow spreads back into the Olympics Friday afternoon as clouds thicken over the Cascades in the afternoon ahead of the next shortwave feature.
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
Light rain and high-elevation snow showers. Increasing moderate winds peak late in the day.
Thursday
Night
Light rain for Hurricane Ridge in the evening (moderate southern parts), ending overnight. Decreasing light to moderate ridgeline winds.
Thursday
Periods of light rain or showers (potentially moderate intensity at times) with higher elevation snow. Increasing moderate ridgeline winds.
Thursday
Night
Moderate to heavy rain and high-elevation snow becomes light and ends during the early morning hours. Moderate ridgeline winds peak in the evening hours.
Thursday
A few rain or high-elevation snow showers. Light to moderate ridgeline winds.
Thursday
Night
Periods of light rain and high-elevation snow, mainly during the evening hours. Light to moderate ridgeline winds.
Thursday
A few rain or highest elevation snow showers, mainly early.
Thursday
Night
Light rain and highest elevation snow tapers or ends overnight. Moderate ridgeline winds mainly before midnight.
Thursday
Mostly cloudy. Isolated snow showers or mixed precipitation in the morning. Light ridgeline and E wind at the Pass.
Thursday
Night
Thursday
Mostly cloudy. Isolated mixed precipitation in the morning. Light to moderate ridgeline and E wind at the Pass.
Thursday
Night
Cloudy with light rain and possibly freezing rain during the evening hours. Moderate ridgeline and light to moderate E wind at the Pass.
Thursday
Periods of light snow in the afternoon. Light to moderate ridgeline winds.
Thursday
Night
Light to moderate snow in the evening becoming light or ending overnight. Light to moderate ridgeline winds.
Thursday
Mostly cloudy with inversions. Light to moderate ridgeline winds.
Thursday
Night
Periods of light snow or mixed precipitation during the evening hours, tapering or ending overnight. Light to moderate ridgeline winds.
Thursday
Partly cloudy with inversions. Light to moderate ridgeline winds.
Thursday
Night
Mixed precipitation possible in the northern part during the evening. Otherwise, mostly cloudy skies. Light to moderate ridgeline winds.
Thursday
Mostly sunny with thin, high clouds. Increasing moderate ridgeline winds. Very mild.
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).