Turnagain Pass

A storm that ended yesterday morning left 1-2 feet of new snow across our region favoring Girdwood, Portage and the Northern side of Turnagain Pass. Several human triggered avalanches occurred on Tincan yesterday on the new/old snow interface. The most notable was a large avalanche in Hippy Bowl that released late in the afternoon on a Southwest aspect. As of now its unknown if this avalanche was natural or triggered remotely from 300+’ away. Earlier in the day observers found easy propagation on facets associated with an old sun crust on a similar aspects and elevation. Prior to this storm surface conditions were variable and consisted of melt/freeze crusts and patches of near surface facets. At this time we do not know how widespread this particular facet/crust combo is across any given slope or how long it will remain reactive. We do know that whumpfing, cracking and recent avalanches were all observed yesterday – and these are signs the snowpack needs more time to adjust. As this new snow settles and becomes more cohesive the size of a slab can increase a day or two following a storm. Today as temperatures increase in the afternoon the likelihood for triggering a larger slab will increase on Southerly aspects later in the day. On shaded aspects with dry loose snow, triggering a slab is likely at any time during the day on slopes steeper than 35 degrees.

An avalanche in Hippy Bowl on a SE aspect of Tincan occured early in the evening and its unknown if it was natural or remotely triggered from the ridge. Earlier in the day observers dug several pits and found some propagation potential on the new/old snow interface, but tests results varied in nearby locations. See video below and click HERE for details about stability tests in these locations. 

Small remote triggered avalanche on NW aspect on Tincay in an area where the snow remained dry all day. Note the large shooting cracks nearby. 

SPRINGTIME WARMING: Yesterday dozens of small wet loose avalanches occurred on South and Southeast aspects in the afternoon. This is very common in the spring on the first day of sun following a storm. Today a thin surface crust has formed on South aspects and it will take more energy to break down this crust. Warmer air has already started to move into the upper elevations and daytime highs could upper 40F’s near sea level. Pay attention to surface warming as daily temperatures will rise above freezing in the afternoon with possiblity of light rain showers. Thin cloud cover can trap the heat and sometimes intensify the affects of solar heating. A superficial crust has formed below 1000’ on all aspects and if this crust softens wet-loose avalanche activity is possible near rocks and in steep terrain. 

Loose snow avalanche triggered by sun and warming on SE aspect of Seattle Ridge in the afternoon yesterday. 

Other avalanche issues to keep in mind: 

Cornices: Daily warming and sunnier weather can make cornices more unstable. As always give cornices plenty of space and limit exposure underneath them.

Dry loose:  Dry loose “sluffing” was triggered on steep shaded terrain features yesterday. Today a fast moving ‘sluff’ could knock you over on larger slopes harboring loose dry snow. 

This new snow fell onto a snowpack with poor structure and several weak layers buried 2-4’ below the old surface. So far there were no avalanches reported on deeper layers of the snowpack. There remains some level uncertainty around the reactivity of these older weak layers from mid winter (facets and buried surface hoar.) Thin snowpack zones such as the Girdwood Valley and the South end of Turnagain Pass are more suspect for this structure, as well as some Northern and Easterly slopes with a generally thinner pack. Trigger points in this situation are often in thinner areas near rocks, but it is also possible to trigger this avalanche problem from areas along ridges.