A deep, cold upper-level low sits off the Pacific Northwest coast early Tuesday as it continues to drift southward. A surface low sits off the SW Washington Coast. With cold air in place and increasing Fraser outflow winds, bringing even more cold air into the lowlands, snow levels will stay below 1000 ft across the region. Generally, light snow showers rotating around the surface low will impact the region through mid-week. Tuesday morning, the heaviest showers will be associated with SE winds targeting the eastern Olympics, southern Washington Cascades, and Mt Hood. These showers pivot northward to focus on the central and northern Washington Cascades and the northern Olympics in the afternoon and evening. Upslope flow along the northern Olympics will be associated with the increased Fraser outflow winds from the NE, which will also bring some elevated winds to western Whatcom County.
The surface low begins to weaken overnight, allowing winds to switch more westerly. This focuses precipitation increasingly on the western slopes of the mountains and creates the potential for weak convergence in the central Washington Cascades.
The upper low lifts back northward on Wednesday, allowing increasing W winds south of the low to focus increasing light to moderate snow shower activity on the southern Cascades. This could bring moderate snowfall to some areas by afternoon (though most areas will receive light snow).
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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Tuesday
Upslope light to moderate snowfall and snow showers focus on the eastern Olympics in the morning and the northern Olympics in the afternoon. Cold.
Tuesday
Night
Light to moderate snow in the eveing becoming light snow showers or flurries overnight.
Tuesday
Mostly cloudy in the morning with a few light snow showers in the afternoon.
Tuesday
Night
Light snow shower activity peaks in the evening, then decreases overnight.
Tuesday
Mostly cloudy in the morning with a few light snow showers in the afternoon.
Tuesday
Night
Light snow shower activity peaks in the evening, then decreases overnight.
Tuesday
Mostly cloudy with light snow showers.
Tuesday
Night
Mostly cloudy with light snow showers.
Tuesday
Mostly cloudy with increasing light snow showers. Light ridgeline and decreasing E wind at the Pass (may become variable in the afternoon).
Tuesday
Night
Light snow shower activity peaks in the evening and decreases overnight. Light ridgeline and light W wind at the Pass.
Tuesday
Mostly cloudy with increasing light snow showers. Light ridgeline and decreasing E wind at the Pass (may become variable in the afternoon).
Tuesday
Night
Light snow shower activity peaks in the evening and decreases overnight. Light ridgeline and light W wind at the Pass.
Tuesday
Light snow or snow showers develop mid-morning and could become moderate late in the day.
Tuesday
Night
Moderate snow possible in the evening, tapers or ends overnight.
Tuesday
Mostly cloudy with light snow showers at times.
Tuesday
Night
Mostly cloudy with decreasing light snow showers.
Tuesday
Mostly cloudy with light snow showers at times.
Tuesday
Night
Mostly cloudy with decreasing light snow showers.
Tuesday
Mostly cloudy with light snow showers. Moderate winds at times the morning.
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).