March 27, 2017

Avalanche Danger Update

Issued Monday, March 27, 2017 at 8:30pm.  This is a general backcountry (recreational) avalanche advisory for Chugach State Park with the Front Range and South Fork Eagle River areas as the core advisory zones.

The chances for significant accumulation of new snow in Chugach State Park increase Tuesday.  Avalanche danger will increase accordingly.  Human triggered avalanches will become likely with any accumulation, with size (from small sluffs to large slabs) dependent on amount of accumulation and wind loading.

The avalanche danger is expected to become heightened to dangerous by midweek.  Temperatures are expected to increase through the week with more snow possible.  These factors could further increase avalanche danger.  Natural avalanches may become possible.

Make sure you know how to identify avalanche terrain, and have at least a basic understanding of how to judge danger. Remember that many popular trails in Chugach State Park cross potentially dangerous avalanche paths.  If conditions are especially dangerous, you may be threatened by avalanche hazard from above (even if you’re on flat, snow-free ground).

The current snow surface is highly variable.  It generally consists, especially in upper elevation avalanche starting zones, of firm to very firm snow.  In many areas a hard wind slab is capped with a layer of heavily faceted snow ranging from several cm to less than a cm thick.  There is also surface hoar in areas that haven’t been exposed to sun and wind (primarily sheltered northerly aspects).  This textbook bed surface and weak layer recipe could be complete with slab, if there’s any significant snowfall in the upper elevations.

Additionally, any new snow will fall on varied hard and slick surfaces: boilerplate windboard , sun crusts, radiation recrystallization crust, and rime ice.  Such surfaces, even without weak layer, could create a reactive weak interface.