An atmospheric river continues to deliver copious amounts of rain to the western slopes of the Cascades, specifically near and north of I-90. The firehouse won't shift much over the next 24 hrs, with Snoqualmie Pass on the periphery of the higher precipitation numbers, and higher confidence of wetter conditions the further north and drier conditions near and south of Highway 12. This isn't as juicy as we've seen with atmospheric rivers, so the conveyor belt of moisture won't push as much moisture over the crest and into the eastern slopes of the Cascades in this iteration. Precipitation will become relatively lighter Wednesday afternoon, before picking up again for the same areas overnight. The frontal boundary may sag a bit south on Thursdy, spreading precipitation to the south WA Cascades. Westerly winds will be strong, to occasionally extreme, especially at upper elevations and in the alpine.
Snow levels will be between 7500'-9000' over the WA Cascades and 12,000' near Mt Hood, where sunnier conditions will persist. Look for snow levels to dip slightly late tonight and Thursday, and we should start to see some wet snow mixing in at upper elevations for the north Cascades.
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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Wednesday
Light to moderate rain, occasionally heavy, on the west slopes of the Olympics. Strong ridgeline winds.
Wednesday
Night
Light to moderate rain, occasionally heavy, on the west slopes of the Olympics. Strong ridgeline winds.
Wednesday
Moderate to occasionally heavy rain. Moderate to strong ridgeline winds.
Wednesday
Night
Moderate to occasionally heavy rain and high elevation snow. Moderate to strong ridgeline winds.
Wednesday
Moderate to occasionally heavy rain. Strong ridgeline winds.
Wednesday
Night
Moderate to occasionally heavy rain. Strong ridgeline winds.
Wednesday
Mostly cloudy with periods of light rain. Drippier west side of the zone and north of Hwy 12. Strong ridgeline winds.
Wednesday
Night
Mostly cloudy with periods of light rain. Drippier west side of the zone and north of Hwy 12. Strong to extreme ridgeline winds.
Wednesday
Moderate to occasionally heavy rain, heaviest in the morning. Moderate W winds at Pass level and ridgeline.
Wednesday
Night
Moderate rain. Strong W winds at Pass level and ridgeline.
Wednesday
Light to moderate, heaviest in the morning. Strong W winds at Pass level and ridgeline.
Wednesday
Night
Light to occasionally moderate rain. Strong W winds at Pass level and ridgeline.
Wednesday
Cloudy with light to occasionally moderate rain near the crest, mostly cloudy with sunbreaks further east. Strong ridgeline winds.
Wednesday
Night
Cloudy with light to occasionally moderate rain near the crest, mostly cloudy further east. Strong ridgeline winds.
Wednesday
Cloudy with light to occasionally moderate rain near the crest, heaviest in the morning, mostly cloudy with sunbreaks further east. Strong ridgeline winds.
Wednesday
Night
Cloudy with light to occasionally moderate rain near the crest, mostly cloudy further east. Strong ridgeline winds.
Wednesday
Mostly cloudy with a chance of light rain near the crest in the morning. Partly sunny to mostly cloudy further east. Strong ridgeline winds.
Wednesday
Night
Mostly cloudy near the crest. Partly to mostly cloudy further east. Strong ridgeline winds.
Wednesday
Partly sunny with periods of high and mid clouds. Strong ridgeline winds.
Wednesday
Night
Partly cloudy with periods of high and mid clouds. 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).