A closed offshore low rotates a frontal boundary northward into Oregon on Sunday. High clouds and ESE winds are already increasing ahead of the system early Sunday. The day will start with filtered sunshine in many areas but expect obscured skies by the afternoon. Moderate ESE winds continue to increase throughout the day in favored areas, particularly near and just west of the Cascade Crest. Light rain and snow start in the Mt Hood area around mid-afternoon, then spread onto the east slopes of the Cascades south of I-90. The initial band of moisture focuses on the southern Washington Cascades during the evening hours and the northern Cascades overnight and slightly favors the east slopes of the Cascades. Winds shift SW in the wake of this initial moisture band as snow levels drop from 4000-4500 down to 3000-3500 ft on Monday. Showers may slowly fill in behind this initial wave of moisture, Sunday night into Monday morning. However, they should increase with more widespread convective showers returning as the low approaches the Oregon Coast during the late morning through 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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Sunday
Filtered sunshine early, then obscured skies from late morning onwards.
Sunday
Night
Periods of light rain and snow. Increasing light to moderate ridgeline winds.
Sunday
Filtered sunshine in the morning, then obscured skies in the afternoon.
Sunday
Night
Increasing periods of light to moderate rain and snow.
Sunday
Filtered sunshine in the morning, then obscured skies in the afternoon. Increasing moderate ridgeline winds.
Sunday
Night
Increasing periods of light to moderate rain and snow. Decreasing light to moderate ridgeline winds.
Sunday
Filtered sunshine in the morning, then obscured skies in the afternoon. Increasing moderate ridgeline winds.
Sunday
Night
Periods of light rain and snow (moderate for the volcanoes). Moderate ridgeline winds in the evening.
Sunday
FIltered sunshine in the morning, then obscured skies in the afternoon. Increasing moderate ridgeline and light to moderate E winds at the Pass.
Sunday
Night
Periods of light rain and snow. Moderate ridgeline winds become light. Light to moderate E wind switches W overnight at the Pass.
Sunday
Filtered sunshine in the morning, then obscured skies in the afternoon. Increasing moderate ridgeline and light to moderate E winds at the Pass.
Sunday
Night
Periods of light rain and snow. Moderate ridgeline winds become light. Light to moderate E wind switches W overnight at the Pass.
Sunday
FIltered sunshine in the morning, then obscured skies in the afternoon. Increasing moderate ridgeline winds.
Sunday
Night
Periods of light rain and snow, overnight. Moderate ridgeline winds become light.
Sunday
FIltered sunshine in the morning, then obscured skies in the afternoon. Increasing moderate ridgeline winds.
Sunday
Night
Periods of light rain and snow, heaviest in the evening. Moderate ridgeline winds become light.
Sunday
Filtered sunshine early, then obscured skies from mid-morning onwards. A chance of light rain or snow late in the day. Increasing moderate ridgeline winds.
Sunday
Night
Periods of light rain and snow, heaviest in the evening. Increasing light to moderate ridgeline winds.
Sunday
High clouds lower and thicken with increasing light rain and snow in the afternoon. Increasing moderate ridgeline winds.
Sunday
Night
Light rain and snow showers. Moderate 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).