A broad trough over the eastern Pacific continues to drive our weather patterns Sunday and give us a feeling of groundhogs day yet again. A series of embedded shortwave systems will pass from south to north off the coast and bring waves of precipitation into the mountains. This is a tricky weather pattern to forecast, however, a few common themes feel more certain. Southerly winds with this storm and low-level easterly flow will favor locations along the east slopes of the Cascades like Ahutanum Meadows, Salmon la Sac, Leavenworth, and Twisp as well as places near the volcanoes. Expect precipitation to pass in waves with pockets of drier weather between. As each disturbance approaches, SE-S winds will increase and peak especially for locations like Mt Baker, Mt Hood, and sites along the Cascade Crest. As the systems pass, winds will shift more southwesterly and decrease. So, that's what we know. The timing and intensity of each wave are much more uncertain.
The first of these systems is already traversing the region from south to north this morning. It will continue to make its way north and spread rain and snow into the North Cascades by mid-morning. Another round of precipitation should follow a similar pattern this afternoon and early evening. A second short wave appears to pass off the coast early Monday morning. This low-pressure feature seems more developed and could drive strong and gusty easterly winds in the Cascade Passes and western mountain valleys. While none of these storms are very significant, they should continue to bring us 2-6 inches of snow in each 12hr period.
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
Cloudy with periods of rain and snow, heaviest in the morning. Moderate S winds becoming SW and strong in the afternoon.
Sunday
Night
Cloudy with periods of rain and snow, heaviest in the evening. Moderate SSW winds decreasing.
Sunday
Cloudy with periods of rain and snow, could be heavy at times. Moderate S winds becoming strong in the afternoon.
Sunday
Night
Cloudy with periods of rain and snow, could be heavy at times. Moderate to strong S winds decreasing overnight.
Sunday
Cloudy with periods of rain and snow. Moderate S winds increasing in the afternoon.
Sunday
Night
Cloudy with periods of rain and snow. Moderate SSW winds decreasing overnight.
Sunday
Cloudy with periods of rain and snow particularly in the morning. Moderate SE winds becoming SW. Periods of gusty winds near the crest.
Sunday
Night
Cloudy with periods of rain and snow. Light to moderate SSW winds turning SSE and decreasing.
Sunday
Cloudy with periods of rain and snow. Moderate E flow at pass level. Light to moderate SE ridgetop winds becoming SSW.
Sunday
Night
Cloudy with periods of rain and snow. Light E flow at pass level increasing. Light to Moderate SW ridgetop winds becoming SSE.
Sunday
Cloudy with periods of rain and snow particularly in the morning. Moderate E flow at pass level. Moderate SE ridgetop winds becoming SW.
Sunday
Night
Cloudy with periods of rain and snow. Light E flow at pass level increasing overnight. Light to moderate SW ridgetop winds becoming SE.
Sunday
Cloudy with periods of rain and snow. Could be heaviest in the eastern mountains. Light to moderate SE winds decreasing.
Sunday
Night
Cloudy with periods of rain and snow. Could be heaviest in the eastern mountains. Moderate SE winds decreasing and becoming S.
Sunday
Cloudy with periods of rain and snow. Could be heaviest near Leavenworth. Moderate S winds becoming SW.
Sunday
Night
Cloudy with rain and snow showers. Moderate SW winds decreasing and becoming S.
Sunday
Cloudy with periods of rain and snow. Moderate S winds becoming SW.
Sunday
Night
Cloudy with periods of rain and snow. Moderate SW winds decreasing and becoming S.
Sunday
Cloudy with periods of rain and snow particularly in the morning. Strong SW winds becoming very strong and gusty in the afternoon.
Sunday
Night
Cloudy with periods of rain and snow. Very strong and gusty SW decreasing gradually overnight.
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).