A significant mountain snow event continues on Monday. A shortwave continues to produce moderate to heavy snow from around I-90 northward early Monday morning. This should gradually exit northward. A renewed push of westerly winds with a cold front moving onshore should ramp the snowfall back up, particularly for the south and central Cascades. Cold air remains in place east of the Cascade Crest with east flow bringing this air through the mountain gaps. The stronger westerly wind surge may start to reverse these winds by late Monday into Monday evening, potentially bringing a rapid warm-up to temperatures just below freezing at Snoqualmie Pass and lower elevations east of the Cascade Crest. Snow amounts remain substantial with another 6-12" of snow expected in many areas on Monday. The heaviest snowfall is expected in the afternoon as an offshore low moves into the area.
SW winds at mid-levels have brought mild air to Mt. Hood, but the cold front arriving by mid-day should allow mid and upper elevations of Mt. Hood to change back to all snow.
Heavy rain and snow continue Monday night as the cold air pool east of the Cascade Crest continues to erode under moderate post-frontal westerly flow accelerating down the east slopes of the Cascades. Temperatures should begin to cool once again after midnight as the low/trough moves eastward and upper-level flow switches northwesterly. Snowfall gradually eases with continued cooling on Tuesday.
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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Monday
Periods of light rain and snow.
Monday
Night
Periods of light rain and snow.
Monday
Periods of light to moderate snow.
Monday
Night
Periods of light snow.
Monday
Moderate to heavy snow.
Monday
Night
Light to moderate snow.
Monday
Heavy snow at Paradise, moderate snow at White Pass, light to moderate snow at Crystal.
Monday
Night
Moderate to occasionally heavy rain and snow.
Monday
Heavy snow. Light E winds at the Pass possibly switching W in the afternoon.
Monday
Night
Moderate snow. Light W winds at the Pass.
Monday
Heavy snow. Decreasing light to moderate E winds at the Pass possibly switching W in the afternoon.
Monday
Night
Moderate snow. Light to moderate W winds at the Pass.
Monday
Light snow at times.
Monday
Night
Light snow at times.
Monday
Moderate to heavy snow.
Monday
Night
Light snow.
Monday
Moderate snow.
Monday
Night
Moderate rain and snow.
Monday
Heavy snow and freezing rain changing to heavy rain and snow. Increasing moderate to strong 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).