Our atmospheric river event moved east of the region as the third wave in the sequence formed a low that moved into British Columbia and a strong front pushed east of our region Tuesday night, leaving post-frontal showers, strong cooling, and decreasing moderate to strong west winds. Expect gernally decreasing post-frontal snow showers primarily from the Mountain Loop south to Mt. Hood. There is some more focused convergence in the Stevens Pass vicinity early Wednesday morning. Convergence should continue to focus on the area from Stevens Pass to the mountain loop as overall snow shower activity maintains primarily in this region during the afternoon and early evening hours before ending. Temperatures dropped 5-15F within several hours behind the front and most locations above 3500 ft are below freezing. Temperatures should continue to fall with snow levels quickly dropping below Snoqualmie Pass level. Areas east of the Cascade Crest and in the southern parts of the Cascades should expect some partial sunshine today.
A ridge of high pressure begins to build back into the region Wednesday night leaving us with partly cloudy skies Wednesday night. Light E flow should start to develop through the mountain gaps overnight.
Thursday, the ridge amplifies over the region. Temperatures increase significantly west of the Cascade Crest while moderate E flow through the mountain gaps keeps significantly cooler temperatures that may barely get above freezing Thursday afternoon at locations such as Snoqualmie Pass. Meanwhile freezing levels should be 10,000-12,000 ft in locations such as the Olympics and 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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Wednesday
Partly cloudy with a chance of snow showers in the morning, then more sun than clouds in the afternoon.
Wednesday
Night
Partly cloudy in the evening, then increasing clouds.
Wednesday
Mostly cloudy with a decreasing chance of light snow showers.
Wednesday
Night
Partly cloudy with increasing high clouds towards morning.
Wednesday
Mostly cloudy with a decreasing chance of light snow showers. Weak convergence likely over King County.
Wednesday
Night
Snow showers lingering into the evening hours. Partly cloudy with increasing high clouds towards morning.
Wednesday
Mostly cloudy with decreasing light snow showers in the morning, then becoming mostly sunny.
Wednesday
Night
Mostly clear in the evening, then increasing high clouds.
Wednesday
Mostly cloudy with a decreasing chance of light snow showers. Convergence in the vicinity of Stevens pass early in the morning may provide some moderate snowfall rates. Decreasing moderate W wind at pass level becoming light late in the day. Strong ridgeline winds in the morning.
Wednesday
Night
Snow showers lingering into the evening hours. Partly to mostly cloudy. Light W wind shifting E in the late evening at pass level.
Wednesday
Mostly cloudy with a decreasing chance of light snow showers. Decreasing moderate W wind at pass level becoming light late in the day. Strong ridgeline winds in the morning.
Wednesday
Night
Snow showers lingering into the evening hours. Partly to mostly cloudy. Light W wind shifting E in the late evening at pass level.
Wednesday
Decreasing light snow showers with mostly cloudy skies.
Wednesday
Night
Partly cloudy early then mostly clearing skies.
Wednesday
Decreasing light snow showers. Mostly cloudy skies. Strong ridgeline winds in the morning.
Wednesday
Night
Partly cloudy with a chance of light snow showers in the evening.
Wednesday
Mostly cloudy with a chance of light snow showers in the morning, then becoming partly cloudy. Strong ridgeline winds in the morning.
Wednesday
Night
Mostly clear early then becoming partly cloudy.
Wednesday
Decreasing light snow showers early in the day with mostly clearing skies in the afternoon.
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).