A complex storm system will impact the Pacific Northwest today, bringing something we haven't seen in awhile - precipitation. The first frontal wave is passing through this morning with some intense snowfall rates with snow levels around 3000', except a bit warmer for Mt Hood and the Olympics. By late morning through mid-day we should see snowfall rates decrease with a break in the heavier precipitation. A secondary upper level feature rounding the base of a broad upper level trough over the NE Pacific will reinvigorate precipitation this afternoon through this evening. The catch will be slightly warmer snow levels in the 3500-4500' for most areas that extends into the early evening. Snow fall looks to be heaviest along the west slopes of the Cascades tonight in Snohomoish and Skagit and perhaps part of Whatcom County thanks to the additional lift associated with a Puget Sound Convergence Zone. With strong W-SW flow and ridgeline winds, you should expect to see snowfall totals taper off rapidly the further east of the Cascade crest you get in this pattern.
After this secondary feature passes through the Cascades Friday evening we'll see snow levels start to plummet after midnight. Look for post-frontal snow showers to continue Friday night and Saturday as much colder air settles into the region and we enter an unstable, convective weather pattern that supports showers. Snow levels will start to fall to near sea-level and even though we'll see the precipitiation forecast decrease relative to today, we'll squeeze out more and fluffier snowfall at these colder temperatures.
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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Friday
Mostly cloudy with light to occasionally moderate rain and snow. Moderate ridgeline winds.
Friday
Night
Light to moderate snow showers. Moderate to strong ridgeline winds.
Friday
Moderate rain and snow, lighter late morning/mid-day and then increasing in the afternoon. Strong ridgeline winds.
Friday
Night
Moderate to occasionally heavy snow showers. Moderate to strong ridgeline winds.
Friday
Moderate to occasionally heavy rain and snow, lighter late morning/mid-day and then increasing in the afternoon. Moderate ridgeline winds.
Friday
Night
Moderate to occasionally heavy snow showers. Moderate to strong ridgeline winds.
Friday
Moderate rain and snow (heaviest Paradise area, lighter Crystal area), lighter late morning/mid-day and then increasing in the afternoon. Strong ridgeline winds.
Moderate rain and snow, lighter late morning/mid-day and then increasing in the afternoon. Moderate S ridgeline winds becoming W in the afternoon. Light east winds at Pass level.
Friday
Night
Moderate snow showers. Moderate to strong W ridgeline and Pass level winds.
Friday
Moderate rain and snow, lighter late morning/mid-day and then increasing in the afternoon. Moderate SW ridgeline winds becoming strong W in the afternoon. Light to moderate east winds at Pass level becoming variable in the afternoon.
Friday
Night
Moderate snow showers. Strong W ridgeline and Pass level winds.
Friday
Light to moderate rain and snow, lighter late morning/mid-day and then increasing in the afternoon. Precipitation heaviest near the Cascade crest. Moderate ridgeline winds.
Friday
Night
Moderate snow showers, heaviest near the Cascade crest. Strong ridgeline winds.
Friday
Light to moderate rain and snow, lighter late morning/mid-day and then increasing in the afternoon. Precipitation heaviest near the Cascade crest. Moderate ridgeline winds.
Friday
Night
Moderate snow showers, heaviest near the Cascade crest. Strong ridgeline winds.
Friday
Light to moderate rain and snow, lighter late morning/mid-day and then increasing in the afternoon. Precipitation heaviest near the Cascade crest. Moderate ridgeline winds.
Friday
Night
Moderate snow showers, heaviest near the Cascade crest. Strong ridgeline winds.
Friday
Moderate to occasionally heavy rain and snow, lighter late morning/mid-day and then increasing in the afternoon. Moderate ridgeline winds becoming strong in the afternoon.
Friday
Night
Moderate to occasionally heavy rain and snow showers. Strong to extreme 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).