Today will mark the beginning of a multi-day atmospheric river (AR) event that should last through early/mid next week. Unlike some of our AR events, this one will feature less of a firehouse and more moderate pulses of precipitation with some relative lulls in between. Confidence in precipitation amounts in on the lower side for the first pulse tonight and then a second wave on Saturday.
For today, we'll likely see moderate to heavy precipitation down at Mt Hood as a warm front stalls out over the region. Lighter precipitation will cross the Columbia during the day, becoming very light the closer you get to the Canadian border. Snow levels will rise quickly in the south and for areas west of the Cascade crest. Stevens Pass and along the east slopes of the Cascades should see temperatures hold relatively steady today.
The first significant wave of precipitation pushes inland tonight and again, we can expect a mix of snow levels depending on which side of the Cascade crest you're on with cooler conditions to the east and milder air to the west. The heaviest precipitation will once again likely be reserved for the Mt Hood area. There's a brief window for potential freezing rain at Snoqualmie Pass, and more likely White Pass this evening before conditions warm. On Saturday, we may see a lull in the morning before more moderate precipitation returns in the afternoon.
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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Friday
Light rain and snow developing during the morning. More moderate precipitation southern slopes of the Olympics. Winds becoming moderate in the afternoon.
Friday
Night
Light to occasionally moderate rain and snow, heavier southern slopes of the Olymipcs. Moderate ridgeline winds.
Friday
Cloudy with periods of light rain or snow. Moderate ridgeline winds.
Friday
Night
Light to moderate rain and snow. Moderate ridgeline winds.
Friday
Cloudy with periods of light rain or snow. Periods of moderate ridgeline winds.
Friday
Night
Light to moderate rain and snow. Moderate ridgeline winds.
Friday
Cloudy with light rain and snow developing during the morning. Moderate ridgeline winds.
Friday
Night
Light to moderate rain and snow, heaviest Paradise area. Chance of freezing rain White Pass area this evening. Moderate ridgeline winds.
Friday
Cloudy with periods of light rain or snow. Light to moderate E-SE Pass and ridgeline winds.
Friday
Night
Light to moderate rain and snow. Light to moderate E-SE Pass and ridgeline winds.
Friday
Cloudy with periods of light rain or snow. Light to moderate E-SE Pass and ridgeline winds.
Friday
Night
Light to moderate rain and snow. Slight chance of freezing rain in the evening. Moderate E-SE Pass and ridgeline winds.
Friday
Cloudy with periods of light rain or snow developing later this morning. Periods of moderate ridgeline winds.
Friday
Night
Light to occasionally moderate rain and snow. Moderate ridgeline winds.
Friday
Cloudy with periods of light rain or snow developing later this morning. Periods of moderate ridgeline winds.
Friday
Night
Light to occasionally moderate rain and snow. Moderate ridgeline winds.
Friday
Cloudy with light rain and snow developing during the morning. Moderate ridgeline winds.
Friday
Night
Light to moderate rain and snow. Moderate ridgeline winds.
Friday
Light rain and snow becoming moderate to occasionally heavy by late morning. Moderate to strong ridgeline winds.
Friday
Night
Moderate to heavy rain and high-elevation snow. Moderate to strong 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).