A powerful low tracks toward the northern tip of Vancouver Island early Tuesday morning, with a bow-shaped frontal system impacting Washington State. Precipitation rapidly increased from White Pass northward in the early morning hours with a warm front lifting northward. Snow levels briefly lowered as the initially dry air mass saturated, giving middle and upper elevations of the central Washington Cascades a shot at 1-2" of wet snow, and the north Cascades a shot at 4-8" before snow levels rose to 7000-8000 ft with the warm frontal passage. The system is accompanied by a 500-mile swath of 50+ mph free air winds at 4500 ft. These will translate into sustained moderate ridgeline winds for most mountain locations, forcing strong orographic effects in addition to the broad-scale lift provided by the potent system. As a result, the west slopes of the Washington Cascades can expect 1-1.25" of water equivalent today, with low-level E winds through early-afternoon resulting in 0.75-1" of water equivalent along the east slopes of the Cascades from White Pass northward. The heaviest precipitation shifts from the northern Cascades to the southern Cascades as the day progresses.
A cold frontal passage in the evening hours pushes the sustained heavy rainfall out of the region in the early evening, with lowering snow levels and lighter snow showers expected to target the W slopes of the Cascades. The frontal passage doesn't shift the wind direction much, resulting in convergence likely targeting the Baker area, potentially 6-12" of snowfall overnight. Snow shower activity increases into the light to moderate range as a shortwave moves into the region Wednesday afternoon, with plenty of instability resulting in more spillover into the lee of the Cascades as well. Snow levels lower to and remain around 2500 ft throughout the day with primarily moderate WSW winds. The convergence potential shifts southward toward the mountain loop as the day progresses.
Weather Forecast
Olympics
West North
West Central
West South
Stevens Pass
Snoqualmie Pass
East North
East Central
East South
Mt. Hood
Use dropdown to select your zone
Tuesday
Moderate rain and snow become light for the northern Olympics. Heavy rain and snow become moderate for the eastern Olympics. Rising snow levels. Moderate ridgeline winds.
Increasing moderate to heavy rain and snow. Rising snow levels. Light ridgeline winds may increase into the moderate range. Light E wind at the Pass switches W during the afternoon.
Tuesday
Night
Decreasing mostly light rain and snow showers. Lowering snow levels. Moderate ridgeline winds. Light to occasionally moderate W wind at the Pass.
Tuesday
Increasing moderate to heavy rain and snow. Rising snow levels. Increasing light to moderate ridgeline winds. Light E wind at the Pass switches W during the afternoon.
Tuesday
Night
Decreasing mostly light rain and snow showers. Lowering snow levels. Moderate ridgeline winds. Light to occasionally moderate W wind at the Pass.
Tuesday
Heavy rain and snow. Rising snow levels. Increasing moderate ridgeline winds.
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).