A deep area of low pressure will sit off the Washington coast today and spin showers over the area in SSW flow aloft. Showers will be the heaviest and most persistent over the Olympic peninsula (especially the southern slopes of the Olympics) today and tonight closer to the low. Showers will be lighter this morning over the Mt Hood area and Cascades but become more widespread and heavier in the afternoon and evening hours. We have a cool unstable air mass overhead and convective showers may be heavy at times, contain graupel, and there's a chance of thunderstorms over the foothills. Freezing levels will rise to 4000-5000' today, but snow levels will plummet to around 3500' during showers. We can expect generally moderate S-SW ridgeline winds over the area, and strong winds for the Olympics and Mt Hood.
Shower activity will taper down after midnight. The low pressure system will pull away from the Pacific Northwest along the coast-line Thursday night and Friday. Weak upper level troughing over the region will renew the threat of afternoon mountain showers. With the flow aloft becoming light out of the north, showers are more likely to fire up over the north Cascades and along the east slopes of the Cascades and slowly drift south. Shower coverage and intensity will be less compared to Thursday. Freezing/snow levels will be a bit warmer on Friday as well.
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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Thursday
Cloudy with light to moderate rain and snow showers, heaviest southern slopes of the Olympics. Sunbreaks possible today. Moderate ridgeline winds becoming strong in the afternoon.
Thursday
Night
Light to moderate rain and snow showers in the evening, then becoming mostly cloudy with light scattered showers after midnight. Moderate ridgeline winds.
Thursday
Cloudy with light scattered rain and snow showers in the morning, becoming light to occasionally moderate showers in the afternoon. Sunbreaks possible today. Moderate ridgeline winds increasing in the afternoon.
Thursday
Night
Light to moderate rain and snow showers in the evening, then becoming mostly cloudy with light scattered showers after midnight. Moderate ridgeline winds.
Thursday
Cloudy with light scattered rain and snow showers in the morning, becoming light to occasionally moderate showers in the afternoon. Sunbreaks possible today. Moderate ridgeline winds increasing in the afternoon.
Thursday
Night
Light to moderate rain and snow showers in the evening, then becoming mostly cloudy with light scattered showers after midnight. Moderate ridgeline winds.
Thursday
Cloudy with light to occasionally moderate scattered rain and snow showers in the morning, increasing and becoming light to moderate showers in the afternoon. Sunbreaks possible today. Moderate ridgeline winds.
Thursday
Night
Light to moderate rain and snow showers in the evening, then becoming mostly cloudy with light scattered showers after midnight. Moderate ridgeline winds.
Thursday
Cloudy with light scattered rain and snow showers in the morning, becoming light to occasionally moderate showers in the afternoon. Sunbreaks possible today. Light to moderate S ridgeline winds increasing in the afternoon. Light east winds at Pass level.
Thursday
Night
Light to moderate rain and snow showers in the evening, then becoming mostly cloudy with light scattered showers after midnight. Moderate SW ridgeline winds. Light west winds at Pass level.
Thursday
Cloudy with light scattered rain and snow showers in the morning, becoming light to occasionally moderate showers in the afternoon. Sunbreaks possible today. Light to moderate S ridgeline winds increasing in the afternoon. Light east winds at Pass level.
Thursday
Night
Light to moderate rain and snow showers in the evening, then becoming mostly cloudy with light scattered showers after midnight. Moderate SW ridgeline winds. Light west winds at Pass level.
Thursday
Mostly cloudy with light scattered rain and snow showers in the morning, becoming cloudy with light to occasionally moderate showers in the afternoon. Periods of moderate ridgeline winds.
Thursday
Night
Light to moderate rain and snow showers in the evening, then becoming mostly cloudy with light scattered showers after midnight. Moderate ridgeline winds.
Thursday
Mostly cloudy with light scattered rain and snow showers in the morning, becoming cloudy with light to occasionally moderate showers in the afternoon. Moderate ridgeline winds.
Thursday
Night
Light to moderate rain and snow showers in the evening, then becoming mostly cloudy with light scattered showers after midnight. Moderate ridgeline winds.
Thursday
Mostly cloudy with light scattered rain and snow showers in the morning, becoming cloudy with light to occasionally moderate showers in the afternoon. Moderate ridgeline winds.
Thursday
Night
Light to moderate rain and snow showers in the evening, then becoming mostly cloudy with light scattered showers after midnight. Moderate ridgeline winds.
Thursday
Mostly cloudy with light scattered rain and snow showers in the morning, becoming cloudy with light to moderate showers in the afternoon. Moderate to strong ridgeline winds.
Thursday
Night
Light to moderate rain and snow showers in the evening, then becoming mostly cloudy with light scattered showers after midnight. 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).