Following several days of high pressure, the Pacific Northwest is transitioning into a very active weather pattern. A very weak disturbance rides over the flattening ridge today, bringing us thickening mid-level clouds with a chance of some very light rain or snow. A strong low-level cold pool east of the Cascade Crest, up to 3000-4000 ft, should continue to drive low-level E flow through low-level mountain gaps, bringing a low cloud layer along with it. The cloud mid-level clouds won't allow enough radiation through to disturb the cold pool significantly on Tuesday, so expect low clouds and cool temperatures to persist most of the day at pass level.
The main pulses of energy associated with the first major storm system this week begin arriving Tuesday night ahead of a warm frontal boundary. Light rain and snow should increase in the evening hours and become moderate to heavy overnight. Winds also ramp up into the moderate to occasionally strong range at ridgeline.
Wednesday should feature the heaviest rain and snow as the occluded front approaches and crosses during the afternoon. Expect many areas to receive heavy rain and snow with snow levels near Snoqualmie Pass level. Snow levels could bump above Snoqualmie Pass level Wednesday morning, but cold E flow at low levels is likely to prevent this from happening. We expect the central Cascades Passes to pick up 8-14" of snow by late Wednesday, with 12-20" expected at Mt. Baker and Paradise.
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
Cloudy with periods of very light rain or snow possible.
Tuesday
Night
Increasing light rain and snow in the evening becoming moderate overnight.
Tuesday
Cloudy with periods of very light snow possible.
Tuesday
Night
Increasing light rain and snow in the evening becoming heavy overnight.
Tuesday
Cloudy with periods of very light rain or snow possible.
Tuesday
Night
Increasing light rain and snow in the evening becoming heavy overnight.
Tuesday
Cloudy with a slight chance of very light rain or snow from late morning onwards.
Tuesday
Night
Increasing light rain and snow in the evening becoming heavy overnight at Paradise, but staying light to moderate at Crystal and White Pass.
Tuesday
Cloudy with a slight chance of very light rain or snow from late morning onwards. Light E winds at pass level.
Tuesday
Night
Increasing light snow in the evening becoming moderate to heavy overnight. Light E winds at pass level.
Tuesday
Cloudy with a slight chance of very light rain or snow from late morning onwards. Light to moderate E winds at pass level.
Tuesday
Night
Increasing light rain and snow in the evening becoming moderate to heavy overnight. Light to moderate E winds at pass level.
Tuesday
Cloudy with a slight chance of very light rain or snow from late morning onwards.
Tuesday
Night
Very light snow developing in the evening and becoming light to moderate overnight.
Tuesday
Cloudy with a slight chance of very light rain or snow from late morning onwards.
Tuesday
Night
Very light snow developing in the evening and becoming moderate overnight.
Tuesday
Cloudy with a slight chance of very light rain or snow in the afternoon.
Tuesday
Night
Increasing light snow.
Tuesday
Cloudy with a slight chance of very light rain or snow in the afternoon.
Tuesday
Night
Increasing light snow in the evening becoming light to moderate overnight. 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).