February 20, 2016

Weekend Avalanche Outlook


Heightened avalanche conditions on specific terrain features.  Evaluate snow and terrain carefully; identify features of concern.


Dangerous avalanche conditions.  Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential.

Avalanche danger is expected to increase through the weekend with moderate to strong winds capable of building fresh wind slabs and the potential for several inches of new snow in the alpine.

Avalanche concerns:

wind-slab-12Winds slabs up to D2 in size are possible above 2500′ on terrain steeper than 35 degrees.  Steep, leeward (primarily west to north) terrain especially along ridges and cross-loaded gully sidewalls is expected to be the most problematic.  Clues to identify include recent wind slab avalanches, areas of deeper snow especially if bulbous in appearance, snow surface texure (etched, or sastrugi), denser/firmer snow that has been wind-packed with underlying weaker snow (hollow sounding-feeling), and cracks radiating from your feet.  Pole probing and quick handpits will be an effective way to get a handle on the wind slab problem.  Moderate to strong winds that picked up Friday and are expected to persist through the weekend, combined with the potential for several inches of new snow in the alpine, will cause the wind slab avalanche danger to increase through the weekend.

persistent-slabPersistent slabs up to D3 in size are possible (low probability, high consequence) above 3000′ on terrain steeper than 35 degrees.  Steep, leeward (primarily west to north) terrain in the upper elevations is expected to be the most problematic.  Be especially wary of large slopes with a deeper and more continuous snowpack.  On such terrain, thinner areas of the snowpack may be trigger points as the weight of a person may more easily penetrate down to persistent weak layers (facets, depth hoar, surface hoar all identified in the Chugach State Park snowpack recently) initiating a fracture.  Digging a full-on snowpit, examining the stratigraphy, and conducting Extended Column Tests (ECT) and Compression Tests (CT) are good means of better understanding the relatively elusive persistent slab problem this weekend.  Please share with us what you find!  The persistent slab problem will be exacerbated this weekend, with increasing danger, due to the added stress from new snow and wind loading.

loose-snowLoose dry avalanches, or “sluffs”, will be likely on steep (35+ degree), relatively sheltered leeward terrain.  Sluffs are expected to be more of a problem Sunday, if/when we receive new snow.  If new snow does not manifest, sluffs will not be much of a problem this weekend due to widespread wind-affected snow.