February 26, 2018

Avalanche Danger Update

New snow and wind has increased avalanche danger in Chugach State Park. Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Natural avalanches possible; human triggered avalanches likely. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Several inches of new snow has already fallen across Chugach State Park, and it’s still snowing (as of 5:00pm). The Indian Pass snotel (2350′) seems to be recording ~8” of new snow. Both the Penguin Peak and Arctic Valley weather stations have recorded southerly winds capable of building wind slabs that may fail naturally, or be especially sensitive to human triggers. Winds have calmed at Penguin, where they were blowing more easterly at their strongest. At Arctic Valley, winds have been significantly stronger and are still blowing moderate with strong gusts.

Avalanche problems:

Widespread D2 (could bury, injure, or kill a person) wind slabs that may be very sensitive to human triggers on terrain steeper than 35* (especially leeward terrain with deeper snow along ridges, near peaks, and in catchment areas) are very likely above 2500′. Be especially cautious around fatter, more bulbous pockets of wind loaded snow. Recent avalanches, shooting cracks, and hollow or punchy feeling snow are obvious clues to wind slab danger. Leeward terrain during the storm has been generally southerly, but winds will become more northerly as the storm clears out into Tuesday. There is ample loose snow for transport. Expect further wind slab development if moderate northerly winds manifest. Wind slabs are expected to behave with soft slab characteristics and break at or below a human trigger.

Persistent slabs to D3 in size are possible on terrain steeper than 35* above 2500′. They may be sensitive to human triggers, or stubborn. This is a less predictable and higher consequence avalanche problem. Two primary persistent slab problems exist, and will be further stressed from the new snow and wind loading:
1. A thin persistent weak layer of facets and buried surface hoar is sandwiched between two wind-packed layers in the upper half to third of the snowpack
2. Large and extremely weak and loose depth hoar exists above the ground, at the base of the snowpack, in most areas.
These persistent slabs may present dangerous hard slab characteristics releasing above and around a human trigger making escape difficult, or releasing remotely from a trigger on adjacent but connected terrain. As these persistent slabs had been more identifiable by a stout wind slab near the surface prior to the recent snow, they are now more deeply buried by fresh and soft snow. It will take thorough stability assessment via snowpits, layer analysis, and stability tests like an ECT to better understand this problem. Whumphing-collapsing and larger recent avalanches that seem to have broken within the old snow will be the most obvious red flags and clues to danger.

Loose dry avalanches, or sluffs, are to be expected on wind sheltered terrain steeper than 40*. While these generally aren’t expected to be inherently large enough to bury, injure, or kill a person; it will be important to keep terrains traps and exposure in mind. A sluff could definitely cause a fall or loss of control that could prove dangerous or deadly considering the terrain.

Cornices, primarily over northerly aspects, are expected to have grown significantly and to be sensitive to human triggers. A cornice fall poses a twofold threat: it could collapse under a person causing them to fall, and the cornice fall could act as a trigger for a subsequent avalanche. Do not approach potentially corniced ridges to look down slope. Give cornices a wide berth as they may break off further back than expected.

Keep in mind that many popular trails in Chugach State Park (e.g. Falls Creek from Turnagain Arm and Powerline from Glen Alps) cross potentially dangerous avalanche paths and are exposed to overhead avalanche hazard. Be mindful of the terrain above you. In the near future, steep upper elevation terrain could release naturally (sending an avalanche into lower elevation and even flat terrain) or be remotely triggered from adjacent terrain.

If you’re planning to recreate in or around avalanche terrain, make sure that you:
1. Know how to identify avalanche terrain (i.e. snow covered terrain steeper than 30*), assess stability, and practice safe travel protocols.
2. Carry essential rescue gear (beacon, shovel, probe) and all other gear and attire necessary for your chosen endeavor and any unforeseen circumstances that might arise.
3. Communicate the plan (i.e. route and expected return time) for your outdoor endeavor to someone that is staying in town and could respond in the case of emergency.

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