Juneau Area Avalanche Advisory
2006-02-05
Showboat - Troy & Mt. Stewart Areas
by Bill Glude, SAAC Observer
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We were in the field both days this weekend, ranging widely to check a variety of sites before the next storm arrives. At low to mid elevations, we continued to find weak snowpacks that are not yet critically loaded. At higher elevations, we found the slab that was very sensitive five days ago has relaxed and our tests and signs of instability all indicated a strong snowpack.

Surface hoar and near-surface faceted grains have formed during the clear weather and will be buried under the new snow except where the wind has blown the surface hoar away. Both snow types form sugary, persistent, weak layers that often release slab avalanches when they are buried by newer snow.

If snowfall and windloading are heavy, an avalanche cycle is likely. Its size will depend on how much snow and wind we get. The weather forecasts are still showing some uncertainty.

If there is much wind transport, new snow, or a thaw preceded by new snow, backcountry travelers should be cautious. If we get heavy snowfall at starting zone elevations, larger slides affecting developed areas are beginning to become a possibility. We will be monitoring conditions closely over the next few days.
Field Notes
Photos
Surface hoar like this in Hilda Meadow on Saturday the 4th formed during the recent clear weather and remains in most wind-sheltered areas. Once buried by new snow, it is a common persistent weak layer. In addition, the cold nights created a strong temperature gradient in the top layers of the snow, producing weak and sugary near-surface faceted grains in the 20 cm below the surface hoar.
On Saturday the 4th, we tested SW aspect slopes in the Showboat - Troy area at about 700m. Like the other low to mid elevation sites we have tested recently, we found weak buried layers of faceted grains. Here, Bill Glude shears a Cutback AK Block on the first gentle jump on the 43 cm facet layer (CAK4Q2) on a 39° test slope. All blocks at low to mid elevations have shown fairly weak snowpack structure lately. These deep weak layers are likely to fracture if the snowpack is loaded rapidly, especially if the near-surface facets and surface hoar fracture first and trigger the deeper instabilities. Marc Scholten photo.
Snowmachiners on Mt. Troy effectively tested almost every slope, including the 45-50° ones, on Saturday the 4th. As far as we could tell, they triggered no slabs, an indication that the older slabs have had time to settle and relax.
Marc Scholten enjoys good powder skiing on Saturday the 4th. As the surface layers of the new snow recrystallize into faceted grains during cool clear weather, their moisture content and density remain the same but the bonds weaken and the snow acquires the characteristic sugary texture of faceted grains. They provide very good travel conditions until they are buried by subsequent snowfall. Then the faceted grains become a dangerously sensitive weak layer.
On Sunday the 5th, we went higher, testing at 900m on Mt. Stewart. On this 39° slope, we found much stronger and less faceted snow than at our lower elevation sites. Windloading was picking up. There was not yet enough windloaded snow to present a problem, but windslabs were beginning to develop.
On Sunday the 5th our test values were all high, mostly in the #6 range (multiple hard jumps). Here Nathan Adams jumps hard as a strong gust of wind drifts another blast of snow into our test site.
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