A large upper trough settled over the region continues to produce enough instability to maintain snow showers for many areas. Moderate NW winds maintain the heaviest showers for Mt Hood and Mt. St Helens, but this shower activity should decrease as the day wears on. Dry and cold NE winds should increase across western Watcom County as a strengthening surface high pressure across interior Canada drives a Fraser River outflow event. Southerly winds converging with the NE outflow have produced convergence from Vancouver Island southeast to around Seattle. A low has formed near the surface and should drift southward as the day progresses. This southward progression should allow a period of light to occasionally moderate snow to form across the northern edge of the Olympics, which is likely to decrease by the afternoon. Light snow showers could also increase somewhat in the Mt. Rainier area during the afternoon. Snow levels should remain near or slightly above sea level across the region throughout the day.
Light snow showers should continue for many areas into the evening areas before the region dries out overnight. Clearing skies should help radiational cooling to produce overnight lows in the teens and single digits for most mountain locations.
Tuesday features a few clouds early, then mostly sunny skies. Temperatures should be well below average for this time of year.
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 snow at times, peaking in the mid to late morning hours.
Monday
Night
Very light snow possible at times, otherwise mostly cloudy.
Monday
Partly to mostly cloudy skies.
Monday
Night
Partly cloudy.
Monday
Partly to mostly cloudy skies with a chance of snow showers.
Monday
Night
Mostly cloudy.
Monday
Mostly cloudy with snow showers.
Monday
Night
Mostly cloudy with a chance of snow showers in the evening.
Monday
Partly to mostly cloudy with a slight chance of an isolated snow shower. Light and variable winds switching E at the Pass.
Monday
Night
Mostly cloudy with a slight chance of snow showers in the evening. Light E winds at the Pass.
Monday
Mostly cloudy with light snow showers at times. Light and variable winds switching E and increasing into the light to moderate range at the Pass.
Monday
Night
Mostly cloudy with a chance of snow showers in the evening. Light to moderate E winds at the Pass.
Monday
Mostly cloudy with a chance of light snow showers.
Monday
Night
Mostly cloudy with a chance of snow showers in the evening.
Monday
Mostly cloudy with light snow developing in the eastern foothills.
Monday
Night
Mostly cloudy with a chance of light snow for the eastern foothills in the evening.
Monday
Mostly cloudy with light snow showers.
Monday
Night
Mostly cloudy with a chance of light snow for the eastern foothills in the evening.
Monday
Moderate snow showers early becoming light by mid-morning.
Monday
Night
Light snow showers through the evening hours, then becoming mostly cloudy.
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).