A frontal system is lifting from the southwest to northeast this morning across Washington State. Steady, heavier precipitation associated with the frontal boundary will shift into the northern Cascades later this morning and post-frontal showers in westerly flow will continue to pepper areas behind the front with moderate to occasionally heavy snowfall rates. Moderate showers will continue through this afternoon, but become a bit more scattered for the central and southern WA Cascades. Strong WSW winds will continue through this afternoon as well. Snow levels will hover around 2500-3500' along the Olympics, Mt Hood and west slopes of the Cascades today and a touch warmer along the east slopes.
A new frontal wave will develop off the Oregon coast later today with a new round of precipitation spreading first into the Mt Hood area this evening, and then as the low passes over central WA tonight, spreading renewed precipitation into the south and central WA Cascades. The Mt Hood area and the far southern WA Cascades including Mt St Helens look to be the hardest hit with this storm, with another 1" or more of snow-water equivalent forecast Saturday night. These areas will also see a warming trend, with snow levels rising to about 5000' and extreme SW winds. There's still some uncertainty regarding how far north the heaviest precipitation will extend. Further north, lighter showers will continue overnight.
We should start to see the frontal boundary associated with the heavier precipitation shift south on Sunday and away from Mt Hood. An upper level trough will shift over the PNW on Sunday, keeping showers in the forecast but with much lighter accumulations than earlier in the weekend. We'll see snow levels creep up a bit, especially along the east slopes of the Cascades on Sunday, into the 4000-4500' range during the afternoon.
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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Saturday
Moderate rain and snow showers, heaviest in the morning. Moderate to strong ridgeline winds.
Saturday
Night
Light to occasionally moderate rain and snow showers. Light to moderate ridgeline winds easing overnight.
Saturday
Moderate rain and snow showers. Moderate to strong ridgeline winds.
Saturday
Night
Light to occasionally rain and snow showers. Light to moderate ridgeline winds easing overnight.
Saturday
Moderate rain and snow showers. Moderate to strong ridgeline winds.
Saturday
Night
Light to occasionally rain and snow showers. Light to moderate ridgeline winds easing overnight.
Saturday
Moderate rain and snow showers, heaviest in the morning. Moderate to strong ridgeline winds.
Saturday
Night
Light to occasionally moderate rain and snow showers in the evening, then light to moderate rain and snow developing around midnight. Moderate ridgeline winds.
Saturday
Moderate rain and snow showers, heaviest in the morning. Strong ridgeline W winds, moderate at Pass level.
Saturday
Night
Light to occasionally moderate rain and snow showers in the evening, then light to moderate rain and snow increasing after midnight. Moderate W ridgeline winds becoming S, W Pass level winds becoming light E.
Saturday
Moderate rain and snow showers, heaviest in the morning. Strong ridgeline W winds, moderate at Pass level.
Saturday
Night
Light to occasionally moderate rain and snow showers in the evening, then light to moderate rain and snow increasing after midnight. Moderate W ridgeline winds becoming S, W Pass level winds becoming light E.
Saturday
Light to moderate rain and snow showers, heaviest in the morning and near the Cacade crest. Moderate ridgeline winds.
Saturday
Night
Light rain and snow showers. Light to moderate ridgeline winds easing overnight.
Saturday
Light to moderate rain and snow showers, heaviest in the morning and near the Cacade crest. Moderate to strong ridgeline winds.
Saturday
Night
Light to occasionally moderate rain and snow showers in the evening, then light to moderate rain and snow increasing after midnight. Light to moderate ridgeline winds.
Saturday
Light to moderate rain and snow showers, heaviest in the morning and near the Cacade crest. Moderate to strong ridgeline winds.
Saturday
Night
Light to occasionally moderate rain and snow showers in the evening, then light to moderate rain and snow increasing around midnight. Moderate ridgeline winds.
Saturday
Moderate to heavy rain and snow showers, heaviest in the morning. Strong to extreme ridgeline winds, strongest during the morning.
Saturday
Night
Moderate to heavy rain and snow. Extreme 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).