April 4, 2018

Avalanche Danger Update

Issued at 9:45pm:

New snow and strong wind has increased avalanche danger in Chugach State Park.  Avalanche danger is expected to remain elevated or increase further Thursday as skies clear, the sun shines, temperatures warm, and wet avalanche problems develop.

A few to several inches of fresh snow are expected in the alpine of Chugach State Park by Thursday.  Strong winds at the upper elevations have created fresh wind slabs on leeward (primarily south and west) aspects, and will add stress to existing persistent slabs where the snowpack remains dry and melt-freeze cycles have not yet initiated.

Bonding and stability of new snow is questionable.  On one hand, spring snow is generally sticky and bonds relatively well.  On the other, variable surface conditions existed prior to the new snow and weak layers (primarily facets over denser snow or crusts) and weak interfaces (slick, icy crusts on solar aspects) are expected to exist.

Warmer temperatures and sunshine, as skies clear, Thursday will weaken the snowpack.

Small, natural wet loose avalanches (aka sluffs and point releases) are expected to be widespread on Thursday as the fresh snow is first subjected to warmth and solar radiation.  While these may be relatively small, they have the potential to entrain a surprising amount of snow as they descend steep terrain and this snow may be like wet concrete.  They could also trigger larger slab avalanches.

Thursday night, freezing temperatures are expected to help stabilize the snowpack and decrease avalanche danger.

As we head into the weekend, a melt-freeze (i.e. corn) cycle is expected to have commenced.  Nightly freezes are expected to stabilize the snowpack, while daily warming will weaken and destabilize it.  Timing is everything in terms of avalanche danger and snow conditions.  Aspect in relation to the sun determines snow stability and quality: not enough warmth and solar radiation and the snow is stable but icy; too much warmth and solar radiation and the snow is too soft, weakened, and unstable.  As hard, frozen snow weakens from warmth and becomes less supportable; avalanche danger increases.

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