Unusually dangerous avalanche conditions exist in the mountains. Please check the avalanche forecast before traveling to or recreating in the mountains.
A cold front moving from NW to SE provides a cutoff from the milder air and heavy rain/snow associated with our multi-day atmospheric river event. This front should pass through Snoqualmie Pass shortly after 2 PM and should be through Mt. Hood by around 7 PM. Expect precipitation rates of 0.1-0.25" per hour for Mt. Hood prior to 7 PM. Very strong downslope winds continue in favored areas along the east slopes of the Cascades. Expect temperatures to continue to cool rapidly at upper elevations and more slowly at lower elevations behind the front. Our attention shifts to convergence zone bands forming rapidly behind the front and currently aimed at the Mountain Loop as of 2 PM on Monday. These bands will shift southward towards the highway 2 and I-90 corridors Monday night. Expect lighter snow showers outside of convergence bands with locally very intense snowfall rates in sharp convergence bands. As temperatures drop and snow-water ratios increase, locations receiving prolonged convergence may pick up more than a foot of snow. Favored locations include western parts of the Cascades East Central zone.
Models indicate a northward shift (toward the North Cascades) of the shower and convergence activity Tuesday morning as a shortwave trough approaches. Multiple convergence bands drop southward as the shortwave moves through Tuesday afternoon. Expect more convective showers with graupel or locally intense snowfall rates likely even in isolated showers, but particularly in convergence bands.
Strong to very strong down-slope and W winds over the Cascade Crest and major mountain gaps winds should gradually ease Monday night into Tuesday morning but should increase slightly Tuesday afternoon with the shortwave feature.
Strong convergence continues in the Central Cascades Wednesday evening before a trough digging slightly to the east of the region reduces or ends shower activity as flow switches NNW overnight. Snow levels should drop to sea level in most areas.
On Wednesday, after a chilly and mostly sunny start to the day with a short-lived ridge building into the region, high and mid-level clouds increase throughout the day ahead of another system.
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
Night
Light snow showers.
Tuesday
Light convective snow showers.
Monday
Night
Light to occasionally moderate snow showers, heaviest southern part.
Tuesday
Light to occasionally moderate convective snow showers, heaviest southern part.
Monday
Night
Moderate rain and snow showers, heavy in convergence bands. Moderate to strong ridgeline winds. Rapidly lowering snow levels.
Tuesday
Moderate convective snow showers, heavy in convergence bands. Moderate to strong ridgeline winds.
Monday
Night
Moderate rain and snow showers at Paradise and White Pass; light at Crystal. Rapidly lowering snow levels. Decreasing strong ridgeline winds at White Pass and near the Cascade Crest.
Tuesday
Moderate convective snow showers at Paradise and White Pass; light at Crystal. Moderate to strong ridgeline winds at White Pass and near the Cascade Crest.
Monday
Night
Moderate snow showers with heavy convergence likely at times. Light to moderate W winds at the Pass. Moderate to strong ridgeline winds.
Tuesday
Moderate convective snow showers with heavy convergence likely at times. Moderate to strong ridgeline winds.
Monday
Night
Moderate rain and snow showers with heavy convergence likely. Snow levels rapidly dropping below the Pass. Moderate W winds at the Pass. Strong ridgeline winds decreasing into the moderate range.
Tuesday
Moderate convective snow showers with heavy convergence likely at times, particularly during the afternoon. Moderate to strong ridgeline winds.
Monday
Night
Light snow showers. Stong ridgeline winds in the evening gradually easing. Strong ridgeline winds decreasing.
Tuesday
Light, but locally intense snow showers. Moderate to strong ridgeline winds. Ridgeline winds increasing into the moderate to strong range.
Monday
Night
Moderate rain and snow showers, locally heavy in convergence bands; strong winds, western part. Light rain and snow showers with strong to very strong ridgeline winds, eastern part.
Light to moderate mountain snow arrives late Wednesday night as a potent shortwave trough with an associated cold front arriving from the NW. A brief period of moderate to strong WSW winds turns W Thursday morning with the cold frontal passage. These winds should efficiently churn out moderate to heavy snow changing to showers on Thursday. More moderate to heavy snow showers are expected as winds turn NW on Thursday night before snow gradually easing as a deeper trough moves over and then east of our region on Friday. Temperatures should stay slightly below average with snow levels 1000-2500 ft throughout the extended forecast period.
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).