The southern end of a cold front brings an abrupt end to the unseasonably warm weather of late. This front brings a 2-3 hour of band moderate rain/snow band with the back edge of the front cutting off steady precipitation around 9-10 AM. E flow should keep precipitation frozen at the passes and east of the Cascades with snow mixing with freezing rain at times near the Cascade Crest. Moderate ridgeline SW winds switch W or WNW behind the front as low-level winds shift W, equilibrating the air masses on both sides of the Cascades to a snow level of around 3000-3500 ft. Ridgeline winds increase and become moderate to strong for mountain gaps, the E slopes of the Cascades, and Mt Hood, which continue at least through Friday night. The main feature to watch as post-frontal rain/snow showers gradually decrease Friday afternoon will be bands of moderate to locally heavy convergence focused between the southern mountain loop and Mt Rainier. This activity continues through the evening hours and wanes overnight.
Snow levels bottom around 2000-2500 ft and only rise slightly during the day on Saturday. Expect WNW flow to keep clouds and moisture banked against the west slopes of the Cascades with light snow showers continuing. Further east, expect partial cloud cover. Ridgeline winds only ease slightly on Saturday, continuing to focus on similar areas.
Moderate rain and snow early transition to decreasing light to moderate rain and snow showers. Moderate ridgeline winds.
Friday
Night
Decreasing light snow showers and moderate convergence (in the evening). Moderate ridgeline winds with strong gusts.
Friday
Moderate rain and snow early transition to decreasing light to moderate rain and snow showers with convergence possible at times. Moderate ridgeline winds. Light to occasionally moderate E wind switches W at the Pass by late morning.
Friday
Night
Decreasing light snow showers and moderate convergence (in the evening). Moderate ridgeline winds with strong gusts. Light to moderate W wind at the Pass.
Friday
Moderate to occasionally heavy rain and snow early transitions to decreasing light to moderate rain and snow showers with convergence possible at times. Moderate ridgeline winds. Light to occasionally moderate E wind switches W at the Pass by late morning.
Friday
Night
Decreasing light snow showers and moderate convergence (in the evening). Moderate ridgeline winds with strong gusts. Light to moderate W wind at the Pass.
Decreasing light snow showers near the Cascade Crest. Moderate ridgeline winds with strong to extreme gusts.
Friday
Light rain and snow through late morning, then decreasing light rain/snow showers and convergence spillover (western part). Increasing moderate ridgeline winds, strong gusts.
Friday
Night
Decreasing light snow showers near the Cascade Crest. Moderate ridgeline winds with strong to extreme gusts.
Friday
Light rain and snow through late morning, then decreasing light rain/snow showers and convergence spillover (western part). Increasing moderate ridgeline winds, strong gusts.
Friday
Night
Decreasing light snow showers near the Cascade Crest. Moderate ridgeline winds with strong to extreme gusts.
Friday
Moderate rain and snow through mid-morning, then decreasing light to moderate rain and snow showers. Strong ridgeline winds with extreme gusts.
Friday
Night
Decreasing light rain and snow showers. Strong ridgeline winds with 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).