A very warm, windy system moved through the Pacific Northwest on Wednesday night. After a cold front passed in the early morning hours on Thursday, the frontal boundary has stalled over southern Washington. This continues to bring heavy rain and snow to the southern half of the Cascades, with a heavy convergence band just north of Stevens Pass bringing very heavy snowfall to that area. This convergence should shift southward over Stevens Pass proper, increasing snowfall rates in the late morning hours. The sustained precipitation is likely to become showery as the day progresses for the northern half of the Cascades, where colder temperatures (1000-2000 ft snow levels) will increase snow accumulations at lower elevations, but precipitation totals will be lighter. Rain should shift to snow at Snoqualmie Pass as cooler air spills into the region (it has already changed back to snow at Stevens Pass). The Southern Cascade Volcanoes should receive the heaviest precipitation (1-2" of water equivalent) during the day, with higher snow levels in the 3500 to 5500 ft range, but slowly lowering.
The atmospheric river lifts slightly northward Thursday night, extending some of the heavier precipitation back into the central Washington Cascades after it drifted south on Thursday. The strong north-south temperature gradient persists, but Thursday night should be the coldest for most areas.
On Friday, a warmer pulse along the frontal boundary moves over the southern half of the Cascades, bringing very heavy precipitation to Mt Hood and the southern Cascade Volcanoes along with strong to extreme winds. Precipitation should be light to moderate in the northern half of the Cascades with continued low snow levels.
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
Decreasing light snow showers. Moderate ridgeline winds in the morning hours.
Thursday
Night
Light to occasionally moderate snow.
Thursday
Moderate snow showers. Moderate ridgeline winds in the morning hours.
Thursday
Night
Moderate snow.
Thursday
Heavy snow showers and convergence, decreasing in the afternoon. Decreasing moderate ridgeline winds.
Thursday
Night
Moderate snow.
Thursday
Heavy rain and snow. Decreasing moderate to strong ridgeline winds.
Thursday
Night
Heavy rain and snow. Moderate ridgeline winds.
Thursday
Heavy rain, snow, and convergence. Lowering snow levels. Decreasing moderate ridgeline winds, strong gusts. Light to moderate W winds at the Pass.
Thursday
Night
Heavy snow. Moderate ridgeline and light-to-moderate W wind at the Pass.
Thursday
Heavy rain, snow, and convergence, becoming showery later in the day. Lowering snow levels. Decreasing moderate to strong ridgeline winds. Light to moderate W winds at the Pass.
Thursday
Night
Heavy snow. Moderate ridgeline and light-to-moderate W wind at the Pass.
Thursday
Light snow showers. Decreasing moderate to strong ridgeline winds.
Thursday
Night
Moderate snow. Light to moderate ridgeline winds.
Thursday
Moderate to heavy rain and snow changing to all snow. Decrasing moderate to strong ridgeline winds.
Thursday
Night
Heavy snow (moderate further east). Moderate ridgeline winds.
Thursday
Moderate to heavy rain and snow. Strong ridgeline winds, extreme gusts.
Thursday
Night
Increasing heavy rain and snow. Moderate ridgeline winds, strong gusts.
Thursday
Heavy rain and snow. Increasing strong ridgeline winds, extreme gusts.
Thursday
Night
Heavy rain and snow. Rising snow levels. Increasing strong ridgeline winds, extreme gusts.
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).