January 21, 2017

Avalanche Danger Update

More snow has fallen than initially forecast, and accumulation is expected to continue through Saturday.  Avalanche danger will increase accordingly, and dangerous conditions are expected to persist through the weekend.

Weekend Avalanche Outlook

Chugach State Park avalanche danger will increase through Saturday due to new snow and wind.

Dangerous avalanche conditions.  Cautious route-finding, conservative decision-making, and careful snowpack evaluation will be essential for traveling safely in and around avalanche terrain.  Natural avalanches are possible, and human triggered avalanches are likely.  Small avalanches may occur in many areas, large avalanches in specific areas, and very large avalanches in isolated areas.

Recognize red flags of avalanche danger.  Acknowledge increased danger from new snow and wind.  Be on the lookout for recent avalanches.  “Whumphing,” or collapsing, and shooting cracks are glaring red flags.

Be mindful of terrain traps, and exposure to overhead avalanche danger.  Avalanches triggered in the upper elevations have the potential to run into lower elevation, even flat, terrain.  Many trails in Chugach State Park cross dangerous avalanche paths (including Penguin Ridge, Falls Creek, Rabbit Creek, Powerline, O’Malley Gully, South Fork Eagle River, and Iditarod-Crow Pass).  A basic level of avalanche awareness, such as that gained through a free or low-cost class, will help you be able to identify problem areas.

Avalanche Problems:

D1-D2 human triggered wind slabs are likely in specific areas: heavily wind loaded leeward terrain steeper than ~35*.  Wind loading is expected to make leeward (primarily west to north aspects) and cross loaded (gully sidewalls) upper elevation terrain (above 2500′) the most sensitive.  Problem areas will feature deeper snow with stiffer snow near the surface, often with shooting cracks and/or a hollow feel.  However, these stiffer wind slabs may be hidden by less wind-affected and looser snow that falls after winds diminish.

D1-D2.5 persistent slabs are possible in specific upper elevation areas steeper than 35*.  Several known natural and human triggered avalanches occurred in Chugach State Park earlier this week.  Some of these were from wind loading of upper elevation leeward terrain during the Saturday-Monday snow event.  There was also modest wind event Wednesday that, due to all the loose snow available for transport, resulted in a significant increase in natural and human triggered avalanche activity.  These older slabs will now be covered by several inches (or even a few feet) of new snow.  They may still prove to be reactive in specific areas: steep terrain features where they overlie persistent weak layers, especially near “sweet spots” like rocks and rollovers, and where the old wind slab is thinner and/or less supportable.  It will take careful snowpack evaluation, like snowpits with stability tests and layer analysis, to understand this problem.

Generally small (D1) loose snow avalanches are possible on wind-sheltered terrain steeper than 35*.  While these are expected to be small and not inherently dangerous, keep terrain traps and exposure in mind.  While these small sluffs won’t bury you, they could make you fall or lose control.

Cornices are still generally small, and aren’t expected to be too problematic this weekend.  However, give theme a wide berth and don’t approach a potentially corniced ridge to look down slope.  Cornice falls pose an inherent hazard, as well as their ability to trigger an avalanche when they fall on a slope.  Earlier this week, natural and human triggered avalanches were observed to have occurred on the leeward side of corniced ridges.


Many avalanche accidents that have happened in Anchorage’s backyard of Chugach State Park could have prevented by basic avalanche awareness.  If you don’t have this level of awareness, here are some online resources to help you start the learning process.  There are also numerous options for getting a real avalanche education locally.  Many of these learning opportunities are even FREE.  Here’s info on a free opportunity at Anchorage REI on Wednesday, February 8 from 6:00-7:30pm.

Chugach State Park is starting to have enough snow for reasonable alpine touring.  Keep in mind that hazards such as superficially covered rocks and vegetation exist.

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