A wide band of NNW-SSE oriented clouds and precipitation precedes an occluded frontal system moving into our area on Saturday. Precipitation spreads throughout the area during the morning hours. Low-level E flow develops and gradually increases as the front moves into the area, creating some light upslope precipitation for the E slopes of the Cascades as well. Light snow increases along with generally SSW winds through the afternoon except in the Mt Hood area where a warm front likely moves through mid-afternoon. Temperatures also gradually increase as the day progresses, allowing snow levels to rise to 1000-3000 ft, but the E slopes of the Cascades and passes remain in the icebox.
A dry sector may exist south of Mt Rainier in the early evening, but moderate precipitation fills in during the late evening hours and overnight as the primary front moves through the region. Moderate SSW ridgeline winds focus on the volcanoes and elevate snow levels west of the Cascade Crest to 2000-4000 ft while low-level E flow peaks in the light to moderate range.
Post-frontal moderate snow showers continue on SW flow on Sunday as an upper low moves toward the coast from the NW. These showers and moderate wind speeds will focus more on the southern half of the Cascades. Snow levels linger around 3000-4000 ft west of the Cascades, but decreasing E flow should keep the passes colder.
Storm totals are likely to be in the 6-24" range for mountain areas through the weekend.
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).