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Avalanche Forecast

Archived

Dec 11th, 2019–Dec 12th, 2019

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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Conditions are changing in the mountains. Temper your excitement, choose conservative terrain, and ease into winter. The first major snow event of the season will bring several feet of snow, particularly in areas near Paradise, and increase the avalanche danger.

Discussion

Paradise is forecasted to receive more water than other areas in the zone, but the story remains the same throughout. A variable early season snowpack, with recent avalanche activity, will become buried throughout the forecast period. A natural avalanche cycle is possible during the height of the storm at higher elevations. Be conservative and ease into terrain by starting with small test slopes and evaluating what is happening with the snow. Tomorrow will be stormy with low visibility, it is not a good day to travel under features that you cannot see the top of. Recognize that until this storm, very low snow conditions existed, and early season hazards will persist despite the new snow.

This storm has the ability to change the avalanche danger quickly over space and time. With periods of high precip rates and fluctuating freezing levels, pay attention to how the storm snow sets up. Is it rightside up or upside down? Are there interfaces within the storm snow as winds or precip rates change? As the snow piles up, a day that starts out as moderate can develop into considerable quickly. Likewise, with high amounts of water forecasted, High avalanche danger could be reached by day’s end in the Paradise area. Anchors will become buried, and slab depth will increase throughout the storm. Pay attention to wind affected snow and look for collapses, cracks, and recent avalanches.

Lots of early season hazards at Rainier before the storm. Photo: Dallas Glass 12/8/19

Snowpack Discussion

Regional Synopsis Coming Thursday, December 12, 2019 

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.