The first in a very wet series of storms moves across the region on Sunday associated with a low pressure center moving across the northern tip of Vancouver Island. A NNW-SSE-oriented front moves across the Cascades during the morning hours bringing rain and snow with a change to increasingly showery precipitation as the day progresses. Cold air east of the Cascades combined with E flow that peaks in the early morning hours will keep the east slopes of the Cascades and the passes cold enough for snow.
Another developing low moving into the region on WSW flow takes a similar track just north of Vancouver Island. It should bring increasingly heavy rain and snow, rising snow levels, and increasing moderate to strong winds Sunday night. Expect Snoqualmie Pass to change from snow to rain by Monday morning with Stevens Pass staying as snow at pass level. Areas of the east slope from I-90 northward should remain primarily snow overnight, but a changeover should progress on Monday as warm air and moisture continue to stream into the region. The heaviest rain and snow should occur during the day on Monday with the firehose of moisture aimed at the central Washington Cascades. However, the firehose appears to be wide with heavy rain and high elevation snow extending from the Canadian Border to Mt. Hood. For Sunday night through Monday, we expect 2-3" for the west slopes of the Cascades, but Snoqualmie Pass and Paradise could get 3-5" as snow levels rise to 5000-7500 ft, but stay a bit colder in the Washington Pass area.
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
Light to moderate rain and snow, becoming light and showery by mid-morning.
Sunday
Night
Moderate rain and snow becoming heavy with rising snow levels and strong winds by the early morning hours.
Sunday
Moderate to heavy rain and snow, becoming light and showery by late morning.
Sunday
Night
Moderate rain and snow becoming heavy overnight.
Sunday
Moderate rain and snow, becoming light and showery by late morning.
Sunday
Night
Moderate rain and snow becoming heavy overnight.
Sunday
Light to moderate rain and snow becoming showery by the afternoon.
Sunday
Night
Moderate rain and snow becoming heavy with strong ridgeline winds overnight.
Sunday
Light to moderate snow becoming showery by the afternoon. Decreasing light to moderate E winds becoming light at the Pass.
Sunday
Night
Light rain and snow becoming moderate to heavy overnight. Light to occasionally moderate E winds at the Pass.
Sunday
Light to moderate snow becoming showery by the afternoon. Moderate E winds becoming light at the Pass.
Sunday
Night
Moderate rain and snow becoming moderate to heavy overnight. Light to moderate E winds at the Pass.
Sunday
Light to moderate snow becoming light and showery by late morning.
Sunday
Night
Light snow becoming heavy overnight.
Sunday
Light snow becoming showery by late morning.
Sunday
Night
Increasing light snow.
Sunday
Light snow becoming showery by early afternoon.
Sunday
Night
Light to moderate rain and snow. Strong ridgeline winds overnight.
Sunday
Periods of light rain or snow. Strong ridgeline wind gusts.
Sunday
Night
Light to moderate rain and snow with elevated snow levels and increasing ridgeline winds becoming strong.
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).