A broad, cold, vertically stacked low-pressure system continues to rotate and wobble over the Pacific Northwest. While the big picture is relatively simple, the movement of the surface low, the scattered-to-isolated nature of snow shower activity, and the potential for convergence or northern Olympic upslope snowfall continue to pose challenges for forecasting. With limited moisture to work with over most of the forecast region, most snow shower activity will be light.
A convergence band has set up at the boundary between moderate Fraser Outflow winds and the winds rotating around a surface low over NW Oregon. This convergence should gradually dissipate in place over the Mountain Loop and the western Highway 2 corridor on Wednesday morning. Otherwise, most snow shower activity focuses on the southern Cascade Volcanoes through the morning hours, where some moderate strength W ridgeline combines with enhanced instability. Some remnants of this shower activity could drift northward into the central Cascades in the afternoon.
A secondary surface low drops southward toward the Oregon Coast Wednesday night (after the initial low dissipates), keeping snow shower activity going over the southern Cascades in particular, while initiating some light E flow for most of the region. This will spawn some very light upslope snowfall or snow shower activity east of the Cascade Crest through the day on Thursday.
Snow levels remain in the 0-1500 ft range with freezing levels generally peaking in the 2500 ft range during mid-day sun breaks.
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 snow showers or flurries at times, mainly in the afternoon.
Wednesday
Night
Scattered light snow showers in the evening, focusing on the northern slopes of the Olympics overnight with upslope light snow.
Wednesday
Mostly cloudy with snow showers or flurries at times, mainly in the afternoon.
Wednesday
Night
A few snow showers in the evening, becoming partly cloudy overnight.
Wednesday
Light snow in convergence banding in the morning, becomes light snow showers in the afternoon.
Wednesday
Night
A few snow showers in the evening, becoming partly cloudy overnight.
Wednesday
Light snow showers focusing more on the southern volcanoes. Shower activity increases in the Mt Rainier area in the afternoon.
Wednesday
Night
Light to occasionally moderate snow showers.
Wednesday
Light snow showers at times, mainly near and west of the Pass. Light ridgeline and W wind at the Pass.
Wednesday
Night
Light snow showers at times. Light ridgeline and E winds at the Pass.
Wednesday
Light snow showers at times. Light ridgeline and W wind at the Pass.
Wednesday
Night
Light snow showers at times. Light ridgeline and E winds at the Pass.
Wednesday
Isolated light snow showers or flurries. Otherwise, partly to mostly cloudy skies with more sunshine further east.
Wednesday
Night
Isolated light snow showers or flurries. Cold.
Wednesday
Isolated light snow showers or flurries. Otherwise, partly to mostly cloudy skies with more sunshine further east.
Wednesday
Night
Light snow showers at times.
Wednesday
Isolated light snow showers or flurries. Otherwise, partly to mostly cloudy skies with more sunshine further east.
Wednesday
Night
Light snow showers (mainly southern part).
Wednesday
Light to occasionally moderate snow showers. Moderate ridgeline winds decrease into the light to moderate range by the afternoon.
Wednesday
Night
Light snow showers. Light to moderate ridgeline winds shifting direction.
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).