Observed new glide avalanches this week: South face, Sunnyside, Hatch Peak. South face of Idaho Peak.
Observed new glide cracks forming: SW face Marmot (Catcher’s Mitt, see photo under avalanche problem 1).
Strong southeast winds Saturday through Tuesday transported available snow and built winds slabs on leeward aspects, west to north. These instabilities were significant, but short lived. On December 8-9 numerous small to large, 1.5 foot deep, human triggered winds slab avalanches occurred on these aspects, on Rae Wallace and Microdot. The avalanche on Microdot caught and carried a person who triggered their airbag, no injuries. Avalanches in Rae Wallace caught and carried skiers who were able to self arrest on the bed surface, no injuries. One large natural wind slab avalanche was observed in Delia Creek. See more information in the observations platform, including a video of a person triggering a wind slab on Microdot here.
|Signal Word||Size (D scale)||Simple Descriptor|
|Small||1||Unlikely to bury a person|
|Large||2||Can bury a person|
|Very Large||3||Can destroy a house|
|Historic||4 & 5||Can destroy part or all of a village|
Glide avalanches continue to be a widespread, low probability, high consequence hazard. These avalanches can fail at the ground, 2-4 feet deep, releasing the entire depth of the snowpack as a unit. Glide avalanches may release at any time, are unpredictable, and can be large enough to bury, injure, or kill a person.
Identifying and avoiding glide cracks is fairly easy and substantially increases your level of safety. You may see other people skiing, riding, or snow machining, near, over, or around glide cracks, however, this is not an indication of stability. Human triggering a glide avalanche is extremely unlikely, and the timing of when a glide releases is highly unpredictable.
Fortunately, avoiding this hazard is fairly easy. Glide cracks visually stand out on the landscape and appear as “brown frowns” (see picture below for reference). Glide cracks can be a single brown frown or a series of cracks. These cracks indicate the snowpack is creeping, which is an extremely slow paced motion down-slope which culminates in the release of the entire snowpack. Glide cracks can exist for seconds or months before the resulting avalanche occurs and is therefore extremely difficult to predict.
While glide avalanches are difficult to predict, their consequences are easy to understand. We can’t tell you what the probability of a given glide avalanche releasing is, but it is something akin to Russian Roulette, which we actually understand the odds of much better. So while you or other people may get away with traveling in or around glide avalanches, and this may happen with some frequency, don’t forget that in doing so, you are risking your life.
A low pressure system moving up the Aleutian chain and into the gulf of Alaska this weekend through mid week is not likely to bring Hatcher Pass much, if any, precipitation. Temperatures will hover around freezing at 3000′ and cool overnight through the weekend. This week’s temperatures are forecasted to cool. Winds should remain light.
Stability is expected to remain the same and stagnate through the weekend and into the early week.
NWS Rec Forecast here.
NWS point forecast here.
State Parks Snow Report and Motorized Access information here.