A split flow pattern leaves the Pacific Northwest with an atypical period of quieter weather for the Thanksgiving holiday into the weekend. Thursday starts cool throughout the region with many valleys and ridgelines mostly in the 20s. An inversion has set up around Washington Pass and offers a sign to come as an offshore high pressure takes an increasing hold on our region. A low cloud and fog deck can be found in many areas throughout the Puget Sound early Thursday.
Mid elevation locations, particularly west of the Cascade Crest will warm quickly on Thursday, thanks to descending air aloft. Areas further north will stay significantly cooler as cooler air rounds the ridge. The result will be freezing levels rising only to 3000 ft in the Mt Baker area compared to 8000 ft around Mt Hood during the afternoon.
Expect more clear skies and rapidly cooling temperatures Thursday night with inversions forming in valley locations and more significantly east of the Cascades.
On Friday, a shortwave feature may bring a few showers to coastal areas and the western slopes of the Olympics along with partly cloudy skies for the west slopes of the Cascades from around Snoqualmie Pass northward. The shortwave will result in cooler temperatures throughout the region on Friday with freezing levels topping out around 3000-4000 ft for Washington State and 5000 ft for Mt Hood.
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
Partly cloudy with low clouds/fog in the morning hours below 1000 ft.
Thursday
Night
Partly cloudy in the evening, then becoming mostly cloudy overnight. Temperature inversion develops with low clouds in the valleys.
Thursday
Partly cloudy with low clouds/fog in the morning hours below 1000 ft.
Thursday
Night
Partly cloudy in the evening, then becoming mostly cloudy overnight. Temperature inversion develops with low clouds in the valleys.
Thursday
Partly cloudy with low clouds/fog in the morning hours below 1000 ft.
Thursday
Night
Partly cloudy in the evening, then becoming mostly cloudy overnight. Temperature inversion develops with low clouds in the valleys.
Thursday
Partly cloudy with low clouds/fog in the morning hours below 1000 ft. Cool start, then becoming mild.
Thursday
Night
Partly cloudy. Temperature inversion develops with low clouds in the valleys.
Thursday
Partly cloudy with low clouds/fog in the morning hours below 1000 ft. Light ridgeline and variable wind at the Pass.
Thursday
Night
Partly cloudy. Temperature inversion develops with low clouds in the valleys. Light ridgeline and variable wind at the Pass.
Thursday
Partly cloudy with low clouds/fog in the morning hours below 1000 ft. Light ridgeline and variable wind at the Pass.
Thursday
Night
Partly cloudy. Temperature inversion develops with low clouds in the valleys. Light ridgeline and variable wind at the Pass.
Thursday
Mostly clear with some high clouds and inversion conditions through the morning hours.
Thursday
Night
Mostly clear. Inversion conditions.
Thursday
Mostly clear with a few high clouds and inversion conditions through the morning hours.
Thursday
Night
Mostly clear. Inversion conditions.
Thursday
Mostly clear with a few high clouds and inversion conditions through the morning hours.
Thursday
Night
Mostly clear. Inversion conditions.
Thursday
Mostly clear. Valley fog early in the day. Cool start, then becoming mild.
Thursday
Night
Mostly clear. Light ridgeline winds become moderate overnight.
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).