The main stories will be extreme, but gradually moderating cold temperatures and a 12-18" snowstorm impacting Mt Hood through this evening.
Mountain temperatures are generally 0 to -30F early Saturday morning east of the Cascades and through the mountain gaps. A -15 mb pressure gradient across the Cascades will increase to around -18 mb by 10 AM before it gradually decreases. The result will be 20-30 mph ridgeline ESE winds through the mountain gaps, with only slightly slower wind speeds at Pass level for places like Snoqualmie. These winds accelerate west of the mountain gaps, creating very strong wind gusts for foothill locations such as North Bend. Temperatures are moderate west of the Cascades with the help of the downsloping winds. Temperatures will gradually moderate in all areas over the next 24 hours.
Meanwhile, a compact system moving toward the Oregon coast brings moderate to heavy snow for Mt Hood Saturday afternoon through the evening hours before tapering to flurries overnight. Snow ratios should be around 13 to 1 with 1-1.5 inches of water bringing 12-18" of snow. The outer fringes of the snowfall may or may not brush Mt St Helens and Mt Adams, but mid and high-level clouds will partially obscure skies for much of the region on Saturday.
Sunday won't be as extreme as Saturday for temperatures and winds, but keep your skin covered on Sunday. Most areas near and east of the Cascade Crest will have low and high temperatures 5-15 degrees warmer, but areas west of the Cascades that have already warmed since Friday may not warm as much. Expect mostly sunny skies and decreasing E winds through the mountain gaps. Temperatures climb into the 10s and low 20s by the afternoon.
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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Saturday
Mostly cloudy with mid and high-level clouds. Cold start with moderating temperatures.
Saturday
Night
Mostly clear. Cold.
Saturday
Filtered sunshine with high-level clouds. Very cold start with moderating temperatures.
Saturday
Night
Mostly clear. Cold.
Saturday
Obscured skies (south) with filtered sunshine (north). Very cold with dangerous windchills in areas exposed to E winds.
Saturday
Night
Decreasing high clouds. Light ridgeline winds (elevated near the Cascade Crest).
Saturday
Cloudy with a chance of snowfall south of Hwy 12 in the afternoon. Snow could moderate intensity south of Mt St Helens and Mt Adams.
Saturday
Night
Cloudy in the evening with a chance of light snow (southernmost part). Skies partially clearing overnight.
Saturday
Obscured skies. Light to occasionally moderate ridgeline and E wind at the Pass. Bitterly cold with dangerous wind chills.
Saturday
Night
Obscured skies in the evening, then clearing overnight. Light to occasionally moderate ridgeline and E winds decrease overnight. Bitterly cold.
Saturday
Obscured skies. Moderate to occasionally strong ridgeline and E wind at the Pass. Winds and gusts may be strongest just west of the Pass. Bitterly cold with dangerous wind chills.
Saturday
Night
Obscured skies in the evening, then clearing overnight. Moderate ridgeline and E winds becoming light to moderate overnight. Bitterly cold.
Saturday
Thin, high clouds. Bitterly cold. Light ridgeline winds slightly enhanced near the Cascade Crest.
Saturday
Night
Skies clearing. LIght winds. Bitterly cold.
Saturday
Obscured skies. Bitterly cold. Light ridgeline winds increase into the moderate range as you near the Cascade Crest.
Obscured skies with a chance of light snow from late morning onwards (southern part). Bitterly cold. Light ridgeline winds increase into the moderate range as you near the Cascade Crest.
Saturday
Night
Cloudy with light snow possible (southernmost part). Light ridgeline winds. Very cold.
Saturday
Light snow at times through mid-morning, then becoming moderate to heavy. Light to moderate ridgeline winds.
Saturday
Night
Heavy snow in the evening tapering to light snow showers overnight. Moderate to strong winds decreasing overnight.
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).