Avalanche Forecast
Issued: Dec 26th, 2018 6:05PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
Robert Hahn,
The bottom line: The sunny skies and fluffy snow may tempt you onto larger terrain, but conditions are dangerous. Winds blowing snow near ridgelines have created large, reactive soft slabs. Stick to lower angle sheltered terrain where you’ll find the best riding.
Summary
Snowpack and Avalanche Discussion
Storm-related avalanche concerns are trending down headed into Christmas Day, but we still don't have a great deal of information about avalanche conditions above 7000 feet where more snow and wind recently impacted avalanche terrain.
As of 12/26, Meadows pro-patrol is still finding weak snow (facets) buried 12/7 in backcountry snowpits between 5500 to 6600 ft on NW through SE aspects, in sheltered terrain roughly 2-3 ft down in the snowpack. The layer is trending toward unreactive. No natural or explosive avalanches have released down to this layer, but we'll continue to track this layer as it evolves over time.
As of 12/26, Meadows pro-patrol is still finding weak snow (facets) buried 12/7 in backcountry snowpits between 5500 to 6600 ft on NW through SE aspects, in sheltered terrain roughly 2-3 ft down in the snowpack. The layer is trending toward unreactive. No natural or explosive avalanches have released down to this layer, but we'll continue to track this layer as it evolves over time.
Regional Synopsis
In most parts of the state, a stout melt freeze crust was formed when it rained to high elevations around Thanksgiving. The one exception to this event was in the East North Zone, where the precipitation from the Thanksgiving storm was all snow. A quick storm at the end of November put a small amount of snow above the melt-freeze crust, and preserved the older basal facets in the northeastern areas.
Cold and clear weather dominated the first week in December, with valley fog and very cold temperatures east of the crest. The surface snow sat around and decomposed. Surface hoar grew large on top of this.
Cold and clear weather dominated the first week in December, with valley fog and very cold temperatures east of the crest. The surface snow sat around and decomposed. Surface hoar grew large on top of this.
Weather Synopsis
A trough centered over the Intermountain West will bring cool N-NW flow to the region as a broad ridge builds offshore on Thursday. The flow will be sufficiently moist to keep low clouds, fog, and a chance of flurries in the forecast. Very weak NW-SE oriented convergence zones will locally enhance snow and cloud in parts of the west slopes Cascades foothills and into the lower passes. Clouds will decrease throughout the day.
Late Thursday night some light snow will arrive in the Olympic mountains from the west as a significant warm front approaches. The Cascades will remain clear and cold.
On Friday, the warm front will be draped parallel to the British Colombia and Washington coastlines. Clouds will lower and thicken with light snow arriving in the Olympics in the morning and in the Cascades by early afternoon.
Friday night the warm front crosses the region bringing moderate to heavy snow changing to rain at Snoqualmie Pass around midnight as easterly flow in the evening switches to westerly, while Stevens Pass will change to rain after midnight.
Late Thursday night some light snow will arrive in the Olympic mountains from the west as a significant warm front approaches. The Cascades will remain clear and cold.
On Friday, the warm front will be draped parallel to the British Colombia and Washington coastlines. Clouds will lower and thicken with light snow arriving in the Olympics in the morning and in the Cascades by early afternoon.
Friday night the warm front crosses the region bringing moderate to heavy snow changing to rain at Snoqualmie Pass around midnight as easterly flow in the evening switches to westerly, while Stevens Pass will change to rain after midnight.
Problems
Wind Slabs
Large wind slabs have formed in the terrain as moderate winds with strong gusts transported 4” of lower density snow on Wednesday with additional snow and wind continuing Wednesday night. You can trigger these slabs on wind-loaded slopes greater than 35 degrees near ridge-lines. Sheltered terrain at lower elevations will have better skiing and riding without the wind slabs.
While not marginal amounts of new snow fell to create a classic storm slab problem, keep in mind that sun changes the slab properties of the upper snowpack and may create this problem on south-facing aspects. When the sun comes out, expect small loose avalanches to occur on steep, rocky, sunny slopes. Don’t let them catch you off guard, especially if you are on slopes that could have dangerous consequences.
While not marginal amounts of new snow fell to create a classic storm slab problem, keep in mind that sun changes the slab properties of the upper snowpack and may create this problem on south-facing aspects. When the sun comes out, expect small loose avalanches to occur on steep, rocky, sunny slopes. Don’t let them catch you off guard, especially if you are on slopes that could have dangerous consequences.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 28th, 2018 6:00PM
