The powerful storm system impacting our region Tuesday afternoon tracks inland into southern British Columbia, while the remains of a moisture-laden frontal system moves ESE across the southern Washington Cascades and Mt Hood areas during the early evening hours. This will bring a few more hours of moderate to heavy rain and snow at higher elevations to these areas before the cold front brings relief in the form of cooling, lowering snow levels, and rain/snow showers.
Although the sustained moderate-to-strong ridgelines will gradually ease, SW winds should have enough momentum to initiate a strong, steady cooling trend. Snow levels lower from around 7000-8000 ft in most areas down to around 3000 ft by early Wednesday morning, lowering further as the morning progresses and settling around 2500 ft as an upper-level trough settles in over the area. Most areas will experience generally light snow showers Tuesday night through Wednesday morning, but the Mt Baker area can expect moderate snow showers and locally heavy convergence. Light to moderate ridgeline winds and snow-shower activity are ramping up ahead of a shortwave disturbance arriving in the late afternoon.
Behind the disturbance, a convergence zone is likely to form in the mountain loop during the evening hours, progressing over Stevens Pass and perhaps dropping south to Snoqualmie Pass for more intense snowfall as ridgeline winds shift west and peak. Expect decreasing light snow showers overnight, with lingering clouds along the west slopes of the Cascades and a few flurries from Snoqualmie Pass northward on Thursday. Expect freezing levels to rise to 3000-4000 ft during the afternoon hours.
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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Tuesday
Night
Increasing light rain and snow showers. Lowering snow levels. Moderate ridgeline winds may decrease to light.
Wednesday
Light to moderate snow showers. Increasing light to moderate ridgeline winds.
Tuesday
Night
Moderate rain and snow showers, locally heavy in convergence. Lowering snow levels. Moderate ridgeline winds.
Wednesday
Moderate to locally heavy snow showers in convergence banding. Increasing light to moderate ridgeline winds.
Tuesday
Night
Light to occasionally moderate rain and snow showers. Lowering snow levels. Moderate ridgeline winds.
Wednesday
Increasing light to moderate snow showers. Increasing light to moderate ridgeline winds.
Increasing light to moderate snow showers. Increasing light to moderate ridgeline winds.
Tuesday
Night
Decreasing mostly light rain and snow showers. Lowering snow levels. Moderate ridgeline winds. Light to occasionally moderate W wind at the Pass.
Wednesday
Increasing light to moderate snow showers. Light to moderate ridgeline winds increase sharply late in the day. Light to occasionally moderate W wind at the Pass.
Tuesday
Night
Decreasing mostly light rain and snow showers. Lowering snow levels. Moderate ridgeline winds. Light to occasionally moderate W wind at the Pass.
Wednesday
Increasing light to moderate snow showers. Moderate ridgeline winds increase sharply late in the day. Light to moderate W wind at the Pass.
Milder weather works its way into the region as a subtle broad ridge pushes the storm track into British Columbia Thursday night through Saturday. The ridge and chances for nice weather likely peak on Friday, before it begins to shift eastward, allowing clouds and a slight chance of precipitation to return to northern Washington as the day progresses on Saturday. Following a few colder midweek days, expect significantly milder temperatures trending back above normal.
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).