A major storm continues to wallop the Pacific Northwest and it will continue to impact the region through Friday.
A parent low near Haida Gwaii has lifted a warm front north to the central Washington Cascades. That front has stalled and continues to bring very heavy rain and snow to the west slopes of the Cascades and Olympics with all snow remaining with entrenched cold air on the east slopes of the Casacades. Snowfall will continue to be dense and heavily rimed in many areas. 1-3" snowfall per hour snowfall rates should continue from the Mountain loop south to Mt. Hood through the morning hours. Rain and snowfall rates will decrease very slightly during the afternoon precipitation should ease for Mt. Hood as the stalled front lifts slightly northward. Snow levels will rise to 5000-6000 ft across the SW Washington Cascades and a battle will play out as the warmer air tries to work north and eastward. Expect sharp differences in temperature across small areas and gradually the warmer air will erode the colder air entrenched east of the Cascade Crest, but some below-freezing temperatures will remain there, particularly north of I-90.
A new low forming at the leading edge of an offshore upper trough will lift the front draped over the region into the North Cascades, focusing the heaviest precipitation from Paradise north to the Canadian Border. Winds will increase and turn increasingly southerly, allowing some E flow to return through the Cascade Passes and we could see a changeover back to more mixed precipitation or even all snow.
The cold front and aforementioned low pressure should cross the Cascades Friday morning with widespread strong winds switching from S to W and heavy precipitation throughout the region. The front should turn precipitation showery by late Friday morning through the afternoon as snow levels lower.
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 snow increasing in the afternoon.
Thursday
Night
Light snow in the morning, becoming moderate in the afternoon. Strong ridgeline winds.
Thursday
Light snow in the morning, becoming moderate in the afternoon.
Thursday
Night
Heavy rain and snow. Strong ridgeline winds overnight.
Thursday
Very heavy snow becoming very heavy rain and snow in the afteroon.
Thursday
Night
Decreasing heavy rain and snow. Strong ridgeline winds.
Thursday
Rain and snow: Very heavy at Paradise and White Pass, heavy at Crystal. Ridgeline winds increasing to strong. Decreasing light to moderate E winds switching W in the afternoon at the pass.
Thursday
Night
Heavy rain and snow at Paradise. Moderate to heavy rain and snow at Crystal and White Pass. Strong ridgeline winds. Variable winds becoming moderate E overnight at the Pass.
Thursday
Very heavy snow. Decreasing light to moderate E winds switching W in the afternoon at the pass.
Thursday
Night
Decreasing heavy snow, possibly mixing with rain at lower elevations west of the Pass in the evening. Strong ridgeline wind gusts. Variable winds becoming moderate E overnight at the Pass.
Thursday
Very heavy snow mixing with sleet, freezing rain and rain in the afternoon.
Thursday
Night
Decreasing heavy rain or freezing rain in the evening, possibly changing back to all snow overnight. Strong ridgeline wind gusts.
Thursday
Moderate snow.
Thursday
Night
Moderate to heavy snow.
Thursday
Decreasing very heavy snow. Strong ridgeline wind gusts.
Thursday
Night
Decreasing moderate to heavy rain or snow. Strong ridgeline winds.
Thursday
Decreasing very heavy snow, sleet, freezing rain, and rain. Strong 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).