An occluded front that passed early Sunday morning and the associated broad trough behind it have underwhelmed in terms of storm dynamics and precipitation. SW flow has brought widely spaced bands of showers to the region on Sunday as a trough moves into the region. We expect more of the same overnight with flow switching more westerly. One organized wave should arrive overnight and might bring some moderate snowfall rates to the west slopes of the mountains of Washington State in the early morning hours. Stevens, Snoqualmie, and Paradise should pick up an additional 2-5" of snow by Monday morning. Temperatures should moderate on the east slopes of the Cascade crest as easterly gradients relax and W flow accelerating down the lee of the Cascades scours the cold air pool while bringing in slightly cooler air aloft.
Snow shower activity should continue to decrease on Monday with mostly cloudy conditions across the region. Expect an additional 1-3" of snow in some areas.
On Monday night, SSW winds increase ahead of a frontal system that arrives late Monday night into Tuesday, spreading moderate to heavy snow across our mountains. We'll have to monitor this system, which is likely to be stronger than Sunday's system.
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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Sunday
Night
Light snow showers. Light ridgeline winds.
Monday
Mostly cloudy with a chance of light snow flurries. Light ridgeline winds.
Sunday
Night
Light snow showers. Light ridgeline winds.
Monday
Light snow showers. Light ridgeline winds.
Sunday
Night
Light snow showers. Light to occasionally moderate ridgeline winds.
Very active weather continues. Post-frontal westerly flow continues to bring additional light snow to the west slopes of the Cascades, with more to the north. Winds shift southerly early Wednesday with a relatively dry start to the day. Snowfall ramps up throughout the day as a front approaches the region and arrives Wednesday evening. The occluded low-pressure center reinforces snowfall as it arrives Wednesday night. Moderate post-frontal snow showers should continue on Thursday with a cold trough over the region.
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).