A weak now drifts northward along the Oregon Coast on Thursday, guided by a stronger upper low further off the coast. This will enable a warm front to continue lifting north across southern Washington State on Monday. The front has brought very heavy snow to the Mt. Hood area, where a very intense precipitation band has set up and should remain over the area into the early afternoon. Low-level easterly flow has kept lower elevations on the east side of the mountain cool, but warmer air streaming in from the SW should eventually win the battle of the air masses by late in the day or this evening, changing snow to rain below 5500 to 6000 ft.
The southern Washington volcanoes should also pick up heavy snowfall during the day. Moderate snowfall can be expected from White Pass north to Snoqualmie Pass, with some light snow making its way north to around Washington Pass during the afternoon. East flow should allow the east slopes of the Cascades to pick up some lighter accumulations while also keeping the passes cold.
The front and the surface low dissipate Monday night. WSW winds will bring the milder air into western Washington and Oregon, beginning to over-run some of the deep cold air pooled east of the Cascade Crest. There will be just enough moisture lingering to potentially create a wintry mess in the early morning hours on Tuesday as warm air over-runs increasingly shallow air. Some freezing rain will be possible near Snoqualmie Pass.
The deeper low continues to spin offshore. Expect a mostly cloudy day with a very weak front approaching the region and touching off some light rain or high elevation snow showers late in the day for the north and central Washington Cascades.
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
Cloudy.
Monday
Night
Cloudy. Milder.
Monday
Cloudy.
Monday
Night
Cloudy. Milder.
Monday
Cloudy northern part. Light to moderate snow, southern part.
Monday
Night
Milder with periods of light rain or snow.
Monday
Heavy snow at Paradise, Mt. St. Helens, and Mt. Adams. Moderate snow at White Pass. Light snow at Crystal. Strong ridgeline wind gusts for Crystal and White Pass.
Monday
Night
Rain and snow rapidly decreasing or ending during the evening hours.
Monday
Light snow, becoming moderate in the afternoon. Decreasing light to moderate E winds at the Pass.
Monday
Night
Milder with periods of light snow. Light E winds at the Pass.
Monday
Increasing moderate snow. Decreasing light to moderate E winds at the Pass.
Monday
Night
Milder with periods of light snow in the evening possibly changing to freezing rain during the early morning hours. Light E winds at the Pass.
Monday
Cloudy and cold with a chance of light snow in the afternoon.
Monday
Night
Cloudy.
Monday
Light to moderate snow.
Monday
Night
Light snow at times, possibly mixing with rain or freezing rain late.
Monday
Moderate snow.
Monday
Night
Light rain or snow, ending during the evening hours. Milder.
Monday
Heavy snow decreasing in the afternoon and possibly changing to rain up to 5500 or 6000 ft from late morning onwards.
Monday
Night
Light rain and snow in the evening, then becoming cloudy.
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).