The Pacific Northwest gets a brief break from snow showers on Thursday night as the broad upper low shifts east of our region, and dry, northerly flow aloft takes its place. Clearing skies will allow temperatures to drop into the 10s and low 20s for many mountain locations. A transient and weak ridge moves through on Friday. That won't mean clear skies as a cold upper low drops south from the Gulf of Alaska and begins to rotate disturbances northward around it. The initial round consists of isolated convective snow showers along the coast and impacting the southern Olympics.
A more significant disturbance rotates into the region late Friday night with rapidly increasing low-level E winds out ahead of it. By Saturday, expect light to moderate snow as a warm front lifts northward, with snow levels gradually rising into the 2000-3000 ft range by the afternoon. The increasing low-level E winds will direct upslope enhancement onto the east slopes of the Cascades.
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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Thursday
Night
Gradually clearing skies. Cold.
Friday
Mostly cloudy with isolated snow showers in the southern Olympics.
Thursday
Night
Clearing skies. Cold.
Friday
Partly to mostly cloudy.
Thursday
Night
Clearing skies. Cold.
Friday
Partly to mostly cloudy.
Thursday
Night
Snow flurries in the early evening with gradual clearing overnight.
Friday
Mostly cloudy
Thursday
Night
Snow flurries in the early evening with gradual clearing overnight. Light ridgeline and W wind at the Pass.
Friday
Mostly cloudy. Light ridgeline and W wind at the Pass.
Thursday
Night
Snow flurries in the early evening with gradual clearing overnight. Light to occasionally moderate ridgeline and light W wind at the Pass.
Friday
Mostly cloudy. Light ridgeline and W wind at the Pass.
Thursday
Night
Partly cloudy in the evening, clearing skies overnight.
Friday
Partly cloudy.
Thursday
Night
Partly cloudy in the evening with a few snow flurries early. Clearing skies overnight.
Friday
Partly cloudy.
Thursday
Night
Partly cloudy in the evening with a few snow flurries early. Clearing skies overnight.
Friday
Partly cloudy.
Thursday
Night
Isolated snow showers. Light to moderate ridgeline winds.
A more significant low rotating northward offshore passes Friday night, with most of the precipitation retreating westward toward the Olympics. A more favorable SW feed of moisture moves into the region and intensifies Sunday night, potentially tapping into more moisture on Monday as the broad trough pushes the frontal band SE. Snow levels should hover around 3000 ft for the mountains of Washington State, but rise to 5000-6000 ft for Mt Hood by Monday.
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).