Tuesday, April 10, 2012
This advisory expires in 24 hours
Natural avalanches are unlikely and human triggered avalanches are possible on all aspects. Natural avalanches are possible and human triggered avalanches are probable on southerly aspects in the afternoon with the increasing solar input.
Decreasing stability on southerly aspects in the afternoon. North and west aspects trending towards stable after new snow settles out, except in thin zones and wind loaded ridges which remain excellent trigger points for future avalanches.
Hatcher Pass received 11″ of new snow on 4/6 and 4/7. Last months tracked up slopes were once again covered with new spring snow. Many sluffs, wet-loose avalanches, and a few soft slabs were observed between 4/7 and 4/10. Whoomping and cracking were observed after the storm as the snowpack attempted to adjust to its new load. Our current issues are twofold. Spring weather conditions are rapidly changing the winter snowpack, shedding surface snow from southerly slopes during the heat of the day. Secondly, buried near surface facets and buried surface hoar lay hidden dormant under variable crusts on north and west aspects waiting for enough stress (ie..new snow) to fail and create more widespread avalanches. A few of these slab avalanches were whittnessed on Sunday.
Three human triggered soft slab avalanches (SS-ASu-R2D1.5–O (x2) and SS-ASu-R2D2-O) were whitnessed on Sunday on north and west aspects. All of these avalanches failed 10″-12″ deep underneath the old crust on buried near surface facets and/or buried surface hoar. Note that buried surface hoar is mysterious, sometimes hard to find, and accounts for widespread avalanche fatalities every year (mostly in Colorado). These persistent weak layers are famous for making their debut this time of year as new snow and an increase in temperature change the existing stability regime.
Watch out for southerly aspects in the afternoon as the stout crusts begin to deteriorate and the new snow adds enough stress to tip the balance of the snowpack. Several wet-loose avalanches (WL-N-R3D2-I) were observed the past several days with the increasing temps. One wet-loose avalanche ripped to the ground on a south face at low elevation. These wet-loose avalanches entrain more snow as they slide and have the ability to take you down and break a leg. Make sure you know which aspect you are on and the time of day! Be careful!
Paying attention to aspect will be critical for safety as the season continues. An entire season of low energy and a stable snowpack is no longer true. There are safe places to ski, but don’t let the new snow cloud your vision and fall into a heuristics trap leading to an accident. A heightened awareness and ability to assess snowpack and changing weather will help keep the outcome of your decisions in the safe zone.