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Avalanche Forecast

Archived

Feb 19th, 2017–Feb 20th, 2017

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

Regions

South Rockies.

Watch for isolated wind slabs and shallow snowpack areas where triggering a deep persistent slab avalanche remains possible.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

MONDAY: Cloudy with isolated flurries, moderate southwest winds, freezing level around 1500 m.TUESDAY: Flurries with 5-10 cm of new snow, strong southwest winds, freezing level around 1500 m.WEDNESDAY: Cloudy, light southwest winds, cooling trend with alpine temperatures around -10 C.

Avalanche Summary

On Sunday, a few size 1-1.5 naturally triggered storm slabs and loose dry avalanches were reported on north and east treeline aspects.On Monday, watch for fresh wind slabs at higher elevations. Also keep in mind that the deep persistent slab problem is a low probability/high consequence scenario that warrants extra caution around large open slopes, especially in shallow snowpack areas.

Snowpack Summary

Light flurries will add to 5-10 cm of recent snow with moderate to strong southwest winds forming deeper deposits and wind slabs. The new snow sits above a thick rain crust below 1900 m. A stiff midpack sits above weak sugary snow near the ground. This deep persistent weakness is primarily a concern in shallow snowpack areas. Watch this video from the South Rockies field team for some recent test results on this layer.

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.

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.