The deep upper low off the Pacific Northwest coastline wabbles back towards the coastline. Following a primarily dry Tuesday evening will enable instability and showers wrapping around the low to move back into the region during the overnight hours. Light to occasionally moderate snow showers will focus initially on Mt Hood and the southern Cascade Volcanoes, then spread into the Mt Rainier area. The upper low spawns a surface feature off the mouth of the Columbia River early Wednesday, focusing a more organized band of light to moderate snowfall (or snow showers) out ahead of it. This precipitation will be accompanied by a shift to increasing light to moderate winds focusing on the same general areas. Low-level ENE winds also create upslope flow and light snowfall for the easternmost part of the Cascades (Mission Ridge). Snow showers and snowfall expand and intensify as the surface low lifts northward Wednesday afternoon, but the heaviest snowfall remains around Mt St. Helens, which could pick up 1 ft of snow by the end of the day. Paradise, Mt Adams, and Mt Hood can expect 2-5" of snowfall while other areas generally can expect up to 3". Expect another helping of similar amounts over the same general areas Wednesday night as the precipitation expands northward.
The upper low morphs into an elongated trough by Thursday, keeping a few weak instability snow showers over the area, but winds should be light, temperatures continue cold, and snowfall amounts quite limited.
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
Night
Decreasing chances of light snow or snow showers.
Wednesday
Mostly cloudy to start, then increasing light snow showers from mid morning onwards.
Tuesday
Night
Mostly clear in the evening, then becoming mostly cloudy in the early morning hours.
Wednesday
Mostly cloudy to start, then increasing light snow showers from late morning onwards.
Tuesday
Night
Partly cloudy with clouds increasing and a chance of light snow in the early morning hours.
Wednesday
Increasing light snow showers.
Tuesday
Night
Increasing light to moderate snow showers starting in the late evening and focusing on the southern Cascade Volcanoes.
Wednesday
Increasing moderate to heavy snow showers focused more on the southern Cascade Volcanoes. Light to moderate ridgeline winds.
Tuesday
Night
Mostly cloudy with light snow developing overnight. Light ridgeline and E wind at the Pass.
Wednesday
Periods of light snow or snow showers. Light ridgeline and E wind at the Pass.
Tuesday
Night
Mostly cloudy with light snow developing overnight. Light to occasionally moderate ridgeline and E wind at the Pass.
Wednesday
Periods of light snow or snow showers. Light to moderate ridgeline and E wind at the Pass.
Tuesday
Night
Mostly cloudy with very light snow possible in some areas.
Wednesday
Increasing periods of light snowfall.
Tuesday
Night
Cloudy with light snowfall in the eastern half of the zone during the evening hours. Increasing light snow throughout the zone overnight.
Wednesday
Increasing light snow or snow showers. Light to moderate ridgeline winds.
Tuesday
Night
Cloudy with light snowfall in the eastern half of the zone during the evening hours. Increasing light snow throughout the zone overnight.
Wednesday
Light to moderate snow showers increasing during the afternoon. Light to moderate ridgeline winds.
Tuesday
Night
Light snow showers in the evening become light to moderate overnight. Increasing light to moderate ridgeline winds.
The aforementioned trough guides another system into California Thursday night. Some moisture from this system will keep the Mt Hood area mostly cloudy with a chance of light snow or snow showers through Friday. Other areas dry out with partly to mostly sunny skies. NW flow develops from Friday night into Saturday. Expect increasing chances of light snowfall for the W slopes of the Cascades with some convergence likely near or south of Snoqualmie Pass on Saturday as a weak disturbance passes to our east.
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).