An upper-level low passes eastward along the Washington/Oregon border Wednesday morning with an associated surface low circulating a compact band of snow and wind around it. The surface low shows up nicely in satellite and radar imagery over the Columbia Gorge at 7 AM on Wednesday. Moderate W winds just to the south of the low will continue to enhance light to moderate snowfall through the morning hours on Mt Hood, while E winds to the north of the low extend the precipitation north to Mt St Helens, Mt. Adams, and the southern ES zone. Light snowfall only makes it as far north as Mt Rainier, but light NNE winds should continue to touch off a few more snow showers along the north slopes of the Olympics until around 10 AM. The northern Washington Cascades are mostly sunny through the morning hours with a band of thinning clouds maintaining some partial cloud cover over the central Washington Cascades. Relatively weak convective buildup across the region induces snow shower activity in the afternoon, with the focus of the action on the southern Cascades and activity tapering as a shortwave ridge approaches Wednesday evening and clear skies across the region overnight.
Clouds begin to lower on Thursday ahead of a shortwave trough. Expect snow showers to develop during the afternoon for the west slopes of the Cascades north of Highway 2.
Snow levels remain in the 1000-3000 ft range throughout the forecast period with a diurnal signal and freezing levels rising to 4000 ft or so during dry periods.
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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Wednesday
Light snow showers early in the day, then becoming partly to mostly sunny.
Wednesday
Night
Mostly clear with thin, high clouds increasing overnight.
Wednesday
Mostly sunny in the morning, then becoming partly cloudy with a chance of an isolated snow shower in the afternoon.
Wednesday
Night
Mostly clear with thin, high clouds increasing overnight.
Wednesday
Mostly sunny in the morning, then becoming partly cloudy with a chance of an isolated snow shower in the afternoon.
Wednesday
Night
Mostly clear with thin, high clouds increasing overnight.
Wednesday
Periods of light snow, decreasing and becoming showery by the afternoon.
Wednesday
Night
Isolated snow showers end during the evening hours with mostly clear skies overnight.
Wednesday
Partly cloudy. Light ridgeline and W wind at the pass.
Wednesday
Night
Mostly clear with thin, high clouds increasing overnight. Light ridgeline and W wind at the Pass.
Wednesday
Partly cloudy. Light ridgeline and W wind at the pass.
Wednesday
Night
Mostly clear with thin, high clouds increasing overnight. Light ridgeline and W wind at the Pass.
Wednesday
Mostly sunny in the morning, then becoming partly cloudy with isolated snow showers in the afternoon.
Wednesday
Night
Isolated snow showers tapering during the early evening, then mostly clear skies overnight.
Wednesday
More sun than clouds in the morning, then becoming partly cloudy with a slight chance of isolated snow showers in the afternoon.
Wednesday
Night
Mostly clear with thin, high clouds increasing overnight.
Wednesday
Periods of light snow focused on areas of upslope flow (southern part). Precipitation transitions to scattered snow showers by the afternoon.
Wednesday
Night
Isolated snow showers tapering during the early evening, then mostly clear skies overnight.
Wednesday
Periods of mostly light snow becoming showery by the afternoon. Decreasing light to moderate ridgeline winds.
Wednesday
Night
Scattered snow showers early, then mostly clearing skies.
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).