A frontal system brought significantly milder (and largely above-freezing) temperatures into the Pacific Northwest by early Sunday. A cold frontal passage late Sunday morning initiated a cooling trend, but only a few of the higher NWAC stations have dipped below freezing. A closed, compact, and well-organized trailing low will track toward the Olympics and cross the central Washington Cascades early Monday. Rain and snow associated with this feature has started for the Olympics on Sunday afternoon. This light to occasionally moderate precipitation should increase across the Cascades overnight. Weak convergence enhancement could develop over western Watcom County around midnight, quickly dropping south to the central Washington Cascades in the early through mid-morning hours on Monday. The cooling trend should continue Sunday night with snow levels dropping from 4000-4500 ft in the evening to around 3000 ft by Monday morning.
Light snow showers gradually decrease across the west slopes of the Cascades on Monday with snow levels gradually rising back up to 3500 ft by the afternoon. Expect minimal spillover onto the east slopes of the Cascades early in the day where partly cloudy skies should develop by the afternoon. Mostly light ridgeline winds decrease behind the departed low, but remain in the moderate range for Mt Hood.
An offshore ridge expands into our region Monday night through Tuesday, bringing increasingly mild conditions. Freezing levels could rise to 9000 ft by Tuesday for Mt Hood although they will only rise to around 6000-6500 ft for the mountains of Washington State. Partly to mostly cloudy skies should linger along the west slopes of the Cascades with clearing skies on the lee slopes.
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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Sunday
Night
Light rain and snow tapering to showers after midnight.
Monday
Mostly cloudy with isolated rain/snow showers in the morning, then becoming partly cloudy in the afternoon.
Sunday
Night
Light to occasionally moderate rain and snow. Some convergence enhancement possible. Decreasing moderate ridgeline winds.
Monday
Light rain and snow showers.
Sunday
Night
Light to occasionally moderate rain and snow. Some convergence enhancement in the early morning hours.
Monday
Decreasing light rain and snow showers with weak convergence enhancement possible in the southern part.
Sunday
Night
Light rain to moderate rain and snow, heaviest at Paradise while Crystal is largely rain shadowed.
Monday
Decreasing light rain and snow showers.
Sunday
Night
Increasing light rain and snow. Light ridgeline and W wind at the Pass.
Monday
Decreasing light snow showers with weak convergence possible. Light ridgeline and W wind at the Pass.
Sunday
Night
Increasing light rain and snow. Increasing ridgeline winds becoming light to moderate. Increasing light W wind at the Pass.
Monday
Decreasing light snow showers with weak convergence possible. Decreasing light to moderate ridgeline winds becoming light. Light W wind at the Pass.
Sunday
Night
Periods of very light rain or snow.
Monday
Isolated light rain or snow showers early, then becoming mostly to partly cloudy.
Sunday
Night
Light rain or snow at times.
Monday
Decreasing light rain or snow showers with more frequent sun breaks in the afternoon.
Sunday
Night
Increasing periods of light rain or snow.
Monday
Light rain or snow showers near the Cascade Crest ending in the morning, then becoming partly cloudy in the afternoon.
Sunday
Night
Increasing light to occasionally moderate rain or snow. Moderate to strong ridgeline winds.
An increasingly strong upper-level ridge just offshore continues to amplify. Expect warming temperatures and clearing skies with snow levels rising above 10,000 ft across the region by Thursday. A system rounds the top of the ridge over British Columbia on Wednesday and could temporarily limit warming or bring some cloud cover to areas near the Canadian border.
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).