A frontal boundary moves through the Cascades around 7 AM Tuesday morning with a band of moderate to locally heavy rain and snow at the leading edge of a cool upper trough. Low-level light E flow Monday night switches W at the Pass, bumping snow levels above Snoqualmie Pass level for much Tuesday. However, cooling aloft should allow for accumulating snow above 3500 ft and the chance of isolated thunderstorms or heavy graupel showers over the area. Steady rain/snow should become showery by the afternoon in many areas, but expect a heavy convergence band to develop over Watcom and Skagit counties, then shift south through the mountain loop by the evening, potentially reaching as far south as northern King County late Tuesday night. Shower activity should gradually decrease in other areas Tuesday night as snow levels drop to 3000 ft or below.
A weak ridge transits the area on Wednesday. Any linger light rain/snow showers should be relegated to the west slopes of the Cascades Wednesday morning, with partial clearing possible precipitation tapers off by the afternoon. Temperatures should be near normal for mid March.
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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Tuesday
Light rain and snow showers. Locally intense.
Tuesday
Night
Decreasing light rain and snow showers.
Tuesday
Moderate to heavy rain and snow in the morning, becoming light and more showery in the afternoon.
Tuesday
Night
Decreasing light rain and snow showers.
Tuesday
Moderate to heavy rain and snow becoming showers with convergence banding from late morning onwards and focused on the northern part.
Tuesday
Night
Moderate rain and snow showers, heavy in convergence shifting southward toward northern King County.
Tuesday
Morning rain and snow heavy at times at Paradise (light to moderate at Crystal and White Pass). Becoming light to moderate showers in the afternoon (locally intense).
Tuesday
Night
Decreasing light to moderate rain and snow showers, heaviest at Paradise.
Tuesday
Moderate rain and snow tapering to showers. Light W wind at the Pass.
Tuesday
Night
Decreasing light to moderate rain and snow showers. Decreasing light W wind at the Pass.
Tuesday
Moderate to heavy rain and snow tapering to moderate showers. Light W wind at the Pass.
Tuesday
Night
Decreasing light to moderate rain and snow showers. Decreasing light W wind at the Pass.
Tuesday
Moderate rain and snow.
Tuesday
Night
Decreasing light rain and snow showers.
Tuesday
Light to moderate rain and snow, tapering to showers. Strong ridgeline wind gusts.
Tuesday
Night
Decreasing light rain and snow showers.
Tuesday
Decreasing light to occasionally moderate rain and snow.
Tuesday
Night
Decreasing light rain and snow showers.
Tuesday
Decreasing moderate rain and snow tapering to showers.
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).