An impressive feed of increasingly subtropical moisture is approaching the Pacific Northwest from Monday through early Wednesday. The first wave in a series of three moves a frontal rain band eastward on Monday. Moderate to heavy rain has started in the Olympics and Mt. Baker area and should spread throughout the Washington Cascades by late morning. Light E flow at low levels should keep the passes cool today while mild air west of the Cascade Crest raises the snow level from 4000-5000 ft in areas not cooled by E flow. Mt Baker should expect a foot of snow today above 4500, but freezing levels are uncertain this morning (4000-4500) and should drop slightly during the afternoon. Paradise could see 8-12" while Snoqualmie and Stevens Passes can expect 3-6" of snow. Mt. Hood should stay mostly dry.
The second wave of precipitation arrives this evening from the SW, bringing even heavier moisture and another increase in winds. The precipitation should spread throughout the region in including Mt. Hood. Many locations can expect 1-2" of snow water equivalent Monday night. This round of precipitation and wind comes with moderate E flow keeping the central Cascades Passes mostly cold enough for snow. Snoqualmie Pass could see a changeover by Tuesday morning or shortly thereafter as the warm SW winds overcome the cooler E flow.
There's really no break as the moisture feed continues ahead of a third wave slated to arrive late Tuesday and Tuesday night. Snow levels continue to climb and most areas except Washington pass should see rain up to 5500-8000 ft while Washington Pass stays cold enough for snow. Moderate to occasionally strong winds should ramp up late in the day.
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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Monday
Light to moderate rain and snow.
Monday
Night
Heavy rain and snow.
Monday
Heavy rain and snow.
Monday
Night
Increasing heavy to very heavy rain and snow.
Monday
Rain and snow developing and becoming heavy from late morning onwards.
Monday
Night
Increasing heavy to very heavy rain and snow.
Monday
Rain and snow developing in the morning and becoming moderate to heavy in the afternoon.
Monday
Night
Increasing rain and snow in the evening becoming heavy to very heavy.
Monday
Rain and snow developing in the morning and becoming moderate in the afternoon. Light E winds at pass level.
Monday
Night
Increasing rain and snow in the evening becoming heavy. Light E winds at pass level.
Monday
Rain and snow developing in the morning and becoming moderate to occasionally heavy in the afternoon. Light E winds at pass level.
Monday
Night
Increasing rain and snow in the evening becoming heavy to very heavy. Light to moderate E winds at pass level.
Monday
Increasing light snow in the morning becoming moderate in the afternoon.
Monday
Night
Moderate snow becoming heavy from late evening onwards.
Monday
Light snow developing in the morning and becoming moderate in the afternoon.
Monday
Night
Increasing rain and snow in the evening becoming heavy.
Monday
Light to moderate rain and snow developing from late morning onwards.
Monday
Night
Increasing rain and snow in the evening becoming heavy.
Monday
Mostly cloudy with a chance of light rain and snow.
Monday
Night
Increasing rain and snow in the evening becoming heavy to very heavy. Ridgeline winds becoming strong.
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).