Problem #1: Wind Slab
Location: All aspects at and above treeline. Shifting winds out of the North and South have loaded all aspects with wind slabs of varying thickness and reactivity. Winds on Wednesday blew out of the South at 15-25mph, loading the northern half of the compass rose. Winds are now blowing out of the north/northwest and will cause areas of fresh wind slab on SW-S-SE aspects in the alpine. Any fresh wind slabs will be cold and reactive to human triggering. Wind slab can be identified by dense, cohesive snow, cracking, and a hollow or drum like feel. Look for wind slab in top and cross loaded terrain like below ridge lines and along gullies. These avalanches could lure riders well onto the slab before failing and could be surprisingly large.
Problem #2: Persistent Slab
Beneath the copious amount of new snow that fell this week lurks a layer of facets sitting above an old rain crust. This weak layer is between 80-120cm deep depending on wind loading. While triggering this deep weak layer is not likely, it will be possible, especially from areas of shallow snowpack near ridgelines and rocks. Propagation along this weak layer could be quite wide, leading to large and deadly avalanches. Heavy triggers like snowmachines and hard landings from skiers will be most likely to trigger this deep weak layer. Use extra caution until this layer has some more time to settle and bond. Make sure to keep wide spacing in your group and anticipate the worst case scenario of an avalanche breaking wider than expected.
Isolated D2-D3 naturals ran during the storm this week, on wind loaded and cross loaded aspects. Crown depths were around 1 meter, running on facets above a rain crust.
Natural D3 avalanche from the storm this week. Chilkat Pass zone, cross-loaded NE aspect at ~4500ft. 2018-12-21
( *star means meteorological estimate )
If you get out riding, please send in an observation!
Start the season with fresh batteries in your beacon, and do a rescue practice with your partners. Always carry a beacon, shovel, and probe, and KNOW HOW TO USE THEM.
Practice good risk management, which means only expose one person at a time to slopes 30 degrees and steeper, make group communication and unanimous decision making a priority, and choose your terrain wisely: eliminating unnecessary exposure and planning out your safe zones and escape routes.
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