A broad shield of precipitation is associated with a moisture stream and a sharp frontal boundary over southern Washington. The frontal boundary divides cold air to the north with mild air over much of the rest of the western US. As of Friday, many locations in the central Puget Sound are receiving light snowfall. The west slopes of the Cascades have generally picked up 8" to 2 ft of snow over the last 24 hours, and the storm continues as the front stalls before gradually drifting southward! This cuts off steadier precipitation over the northern portions of the forecast region, where snowfall has been less intense. Very heavy precipitation is focused on the southern Washington Cascades and will continue throughout the day in this area. Snow levels should hover around 4000-4500 ft around Mt Rainier, but will be 1000 ft higher for Mt St Helens and Mt Hood. Further north, snow levels are near the surface in the central Cascades, with moderate to heavy snowfall decreasing throughout the day. Winds will be strong around Mt Hood and moderate over the southern Washington Cascades, Snoqualmie Pass, and the east slopes of the Cascades.
Precipitation continues to decrease over most of Washington State as the front continues to drift southward, but remains moderate to heavy for the southern Washington Cascades. Mt Hood enters the line of fire with around 1.5" of water equivalent expected. Snow levels start high (6500 ft), but lower to 4500 ft overnight.
A subtle trough arriving from the NW cuts off the sustained snowfall by Saturday morning, with light snow showers and convergence continuing throughout the day. Some areas of the central Washington Cascades could receive some locally moderate snowfall rates early in the day in convergence bands. Snow levels will be near sea level.
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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Friday
Light snow gradually decreasing.
Friday
Night
Scattered light snow showers.
Friday
Light snow tapering early, then on-and-off light snow showers.
Friday
Night
Light snow showers.
Friday
Moderate snow becoming light by mid-morning. Snow will be heavier further south.
Friday
Night
Light snow showers and weak convergence bands.
Friday
Heavy rain and snow. Moderate ridgeline winds.
Friday
Night
Heavy snow in the evening, decreasing from north to south overnight. Moderate ridgeline winds.
Friday
Decreasing moderate to heavy snow. Mostly light ridgeline and W wind at the Pass.
Friday
Night
Light snow showers and weak convergence. Light to occasionally moderate ridgeline and light W wind at the Pass.
Friday
Decreasing heavy snow. Moderate ridgeline and increasing light W wind at the Pass.
Friday
Night
Light to moderate snow decreases in the evening, becoming light and showery overnight. Moderate ridgeline and light to moderate W wind at the Pass.
Friday
Light snow decreases, tapering to showers.
Friday
Night
Isolated light snow showers. Moderate ridgeline winds at times.
Friday
Decreasing moderate to heavy snow. Moderate ridgeline winds.
Friday
Night
Decreasing light snow in the evening, then light snow showers overnight. Moderate ridgeline winds.
Friday
Heavy snow. Moderate ridgeline winds, strong gusts.
Friday
Night
Moderate to heavy snow in the evening becoming light overnight. Moderate ridgeline winds.
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).