It's a pretty quiet start across most of the forecast region this morning. An offshore trough will split in half today sending the bulk of the system south to California. The leftover short wave system will push into the PNW today but it won't be in much of a hurry. Sunday, most of the precipitation will focus on the North Cascades in the morning. Expect stormy conditions with periods of heavy rain/snow and strong and gusty winds. As the system slowly starts to move, the stormy weather will spread into the Olympics and Mountain Loop Highway areas. A few showers could make their way to Wa Pass, Stevens Pass, and Snoqualmie Pass late in the afternoon, but most other areas should stay dry. Even if you don't see any precipitation during the day, you'll notice the increasing clouds and gusty winds. The strongest wind speeds should focus on Hurricane Ridge, Mt Baker, Mt Saint Helens, and Mt Hood during the day.
As we head into the evening, precipitation continues to spread south and east. A cold front will bring a concentrated several hours of precipitation that easily spills over to the eastern forecast zones. As temperatures cool, snow should quickly return to the Passes. The heavier precipitation doesn't last long. The system shifts east of the mountains, precipitation turns showery, and winds start to decrease. A short-lived Puget Sound Convergence Zone could form overnight and target Stevens and possibly Snoqualmie Pass.
Lingering low level moisture and onshore flow should keep the western zones and passes cloudy for most of Monday with a few light showers. However, weak zonal flow will allow for drier air to settle into the region. While we should see showers quickly coming to a close and clouds breaking, it doesn't look like we go full "bluebird." Our next system should arrive 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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Sunday
Becoming stormy with strong and gusty SSW winds combined with periods of heavy precipitation.
Sunday
Night
Mostly cloudy with a few showers in the evening. Light to moderate W winds decreasing.
Sunday
Becoming stormy with strong and gusty SSW winds combined with periods of moderate to heavy precipitation.
Sunday
Night
Showers, heaviest in the evening. Light to moderate W winds.
Sunday
Cloudy with rain and snow developing during the day. Moderate to strong and gusty SSW winds.
Sunday
Night
Rain and snow in the evening, becoming showery. A Puget Sound Convergence Zone near the Hwy 2 corridor. Moderate W winds decreasing.
Sunday
Becoming cloudy. A few isolated showers possible late in the afternoon. Moderate to strong and gusty SW winds.
Sunday
Night
Rain and snow in the evening with cooling temperatures. Moderate to strong and gusty W winds decreasing.
Sunday
Becoming cloudy. A few showers in the late afternoon. Winds becoming SW moderate and gusty.
Sunday
Night
Rain and snow, heaviest in the evening. Becoming more showery. A Puget Sound Convergence Zone could impact Stevens Pass. Moderate and gusty W winds decreasing.
Sunday
Becoming cloudy. A few showers in the late afternoon possible. WSW winds becoming moderate and gusty.
Sunday
Night
Rain and snow, heaviest in the evening, becoming more showery overnight. A Puget Sound Convergence Zone could clip Snoqualmie Pass overnight. Moderate and gusty W winds decreasing.
Sunday
Cloudy with rain and snow mainly in the afternoon. Moderate to strong and gusty SW winds.
Sunday
Night
Rain and snow in the evening, becoming showery. Moderate to strong and gusty W winds decreasing.
Sunday
Becoming cloudy. A few showers possible, mainly in the northern half of the zone in the afternoon. Moderate to strong and gusty SW winds.
Sunday
Night
Rain and snow, mainly in the evening, becoming scattered showers overnight. Strong and gusty W winds decreasing.
Sunday
Increasing clouds. Moderate to strong and gusty SW winds.
Sunday
Night
Rain and snow showers mainly in the evening. Moderate to strong and gusty SW winds decreasing.
Sunday
Mostly sunny to start the day with increasing clouds. Very windy. Strong and gusty SW winds increasing in the afternoon.
Sunday
Night
Rain and snow developing in the late evening. Very strong and gusty SW winds turning W and decreasing slightly.
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).