The new year starts with a pattern shift. A weak low-pressure center tracking off the Oregon Coast brings an end our recent ridge of high pressure. Light rain and higher elevation snow have started early Thursday in the Mt Hood region as a band of mostly light precipitation moves northward on southerly flow aloft. Precipitation type becomes tricky as this moisture moves into deeper cold air pools along the east slopes of the Washington Cascades and passes. We expect precipitation to commence as light snow in these areas, but as rain and higher-elevation snow further west. Precipitation should reach the central Washington Cascades during the afternoon.
The low-pressure center approaches western Washington on Friday night, spreading increasing light to moderate precipitation throughout the Cascades in the evening, intensifying further overnight. Moderate WSW winds should begin to erode the cold air pool in areas closer to the Cascade Crest, resulting in a change from snow to rain and freezing rain at Snoqualmie Pass during the evening hours, with that transition likely occurring overnight at Stevens Pass. Mission Ridge and Washington Pass are likely to stay snow.
Moderate rain and snow continue to focus on the west slopes of the Cascades Friday morning, becoming light in the afternoon as the low-pressure center exits the area. This precipitation falls as snow above 5500-6500 ft, except in portions of the eastern North Cascades, where the cold pool lingers.
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
Cloudy with a chance of light rain or snow in the southern and eastern Olympics during the afternoon.
Thursday
Night
Increasing light rain and higher elevation snow.
Thursday
High clouds lower and thicken. Mild.
Thursday
Night
Increasing light rain and snow.
Thursday
High clouds lower and thicken. Mild.
Thursday
Night
Increasing light rain and snow become moderate overnight.
Thursday
High clouds lower early, then increasing chances of light rain, high elevation snow, or even freezing rain near the Cascade Crest.
Thursday
Night
Increasing moderate to locally heavy rain, higher elevation snow, and a wintry mix at times near the Cascade Crest.
Thursday
High clouds lower and thicken in the morning, then a chance light snow develops in the afternoon. Increasing light ridgeline and E wind at the Pass.
Thursday
Night
Increasing light to moderate snow, potentially mixing with freezing rain overnight. Light ridgeline and E wind at the Pass.
Thursday
High clouds lower and thicken in the morning, then a chance light snow develops in the afternoon. Increasing light ridgeline and light to moderate E wind at the Pass.
Thursday
Night
Increasing light to moderate snow changing to rain, and freezing rain by late evening. Light to moderate ridgeline and E wind at the Pass.
Thursday
High clouds lower and thicken. Inversion conditions continue.
Thursday
Night
Increasing light snow.
Thursday
High clouds lower and thicken in the morning. A chance of light snow in the afternoon.
Thursday
Night
Increasing light snow. Freezing rain possible in western parts.
Thursday
Lowering clouds early, then light rain, snow, or freezing rain at times.
Thursday
Night
Increasing light to moderate rain, higher elevation snow, and freezing rain.
Thursday
Increasing light to moderate rain and higher elevation snow. Moderate ridgeline winds.
Thursday
Night
Moderate rain and higher elevation snow. 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).