A cool upper trough remains over the Pacific Northwest region, bringing scattered snow showers and convergence snowfall to the region. Winds rotating around the upper trough should gradually ease in the southern parts of the forecast region as the trough settles deeper into the region and flow shifts gradually more northerly. This should shift the heavier bands of convergence for the central Washington Cascades to the Mt. Rainier area where we expect 3-8" of snowfall Sunday night. Light to moderate snow showers should also continue to provide accumulations for Mt. St. Helens and Mt. Hood. A Canadian air mass continues to move into the region, providing cooling aloft. That cooling should move into the lowlands on Monday as a modified arctic front moves southward at the leading edge of the Fraser River outflow.
Monday should be dry in the Mt. Baker area with more moisture available for snow shower activity further south. Snow showers should be heaviest around Mt. Hood. The modified arctic front may produce a period of light to moderate snowfall Monday morning with the greatest amounts likely in the foothills of the range. As this front moves southward, it could serve as the focal point for converging air masses and increased snowfall from Mt. Rainier to Mt. Hood. Daytime heating is also likely to help produce some graupel showers during the afternoon. E flow developing through the mountain passes should intensify and the E-NE winds may touch off some light snowfall for the Wenatchee Mountains and other points well east of the Cascade Crest that should continue into Monday evening before the region dries out with clear skies and cold temperatures.
Tuesday features very light NNE winds aloft and light to occasionally moderate E winds continuing through the mountain gaps. Expect below normal temperatures with a slight chance of isolated afternoon showers due to daytime instability.
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 at times with a period of moderate snow possibly developing due to upslope flow in the early morning hours.
Monday
Light upslope snowfall, mainly during the morning hours, then becoming partly cloudy later in the day.
Sunday
Night
Isolated very light snow showers.
Monday
Mostly sunny.
Sunday
Night
Light snow showers with heavier bands possible in convergence, southern part.
Monday
Partly cloudy with a chance of snow showers.
Sunday
Night
Convergence likely impacting the Mt. Rainier area with moderate snow possible at Paradise and Crystal and light to moderate snow at White Pass. Strong ridgeline wind gusts near the Cascade Crest should gradually ease.
Monday
Light snow showers and convergence.
Sunday
Night
Light snow showers with heavier bands possible in convergence. Light W winds at the Pass.
Monday
Light snow showers with plenty of sun breaks. Increasing light to occasionally moderate E wind at the Pass.
Sunday
Night
Light snow showers with heavier snwofall rates possible at times in convergence. Light W winds at the Pass.
Monday
Light snow showers with plenty of sun breaks. Increasing light to moderate E wind at the Pass.
Sunday
Night
Light snow showers.
Monday
Light snow showers and frequent sun breaks.
Sunday
Night
Light snow showers and convergence spillover mainly near the Cascade Crest.
Monday
Light snow showers with steadier upslope snowfall in areas further east such as Mission Ridge.
Sunday
Night
Periods of light to occasionally moderate snowfall to areas close to the Cascade Crest due to convergence spillover.
The upper trough swings into the desert southwest Tuesday night, leaving the region under cool northerly flow with light E winds through the mountain gaps, light E flow at low levels, and very cold temperatures at the surface. Wednesday should be clear and cool. Weak disturbances may try to ride down the back side of a narrow ridge extending up to the Gulf of Alaska. This could bring some clouds and a slight chance of flurries by Thursday.
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).