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Avalanche Forecast

Archived

Nov 20th, 2015–Nov 21st, 2015

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Glacier.

It is looking like a beautiful and cold weekend. As the sun lures you out, keep in mind that there are still instabilities in the snowpack. Be careful at ridgecrests where windslabs exist, and avoid thin spots where deep facets may be triggered.

Weather Forecast

Today should be clear and cold. Temps will be around ~15'C with moderate Northerly winds. Saturday will be slightly warmer, but windier. On Sunday a weather system will bring increasing cloud and flurries by Monday.  Freezing levels may rise to 1500m.

Snowpack Summary

Recent observations suggest that the ~1m of storm snow is settling and bonding. Strong S-SW winds at treeline and above continue to load lee features, forming deep loaded pockets. Surface hoar layers down ~1m and 1.5m are still a concern but becoming more stubborn and hard to find. On high elevation N/NE aspects, there is a weak facetted base.

Avalanche Summary

Avalanche activity continued yesterday, but was limited to steep terrain. Several size 2-2.5 slab avalanches were likely triggered by wind-loading. During the major avalanche cycle earlier this week there were avalanches to size 3.5 with some avalanches stepping down to deeper layers, including the Nov 5 surface hoar and the basal facets.

Confidence

Due to the number of field observations

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.