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Avalanche Forecast

Archived

Feb 16th, 2015–Feb 17th, 2015

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

Regions

South Rockies.

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Confidence

Good

Weather Forecast

A mix of sun and cloud is for Tuesday and Wednesday with increase cloud cover expected for Thursday, but no precipitation expected. Freezing levels remain in valley bottoms for Tuesday before possible above freezing alpine temperatures on Wednesday; however, cooler temperatures expected again for Thursday, and freezing levels expected to drop to valley bottoms overnight throughout the forecast period. Generally light northwesterly winds are expected with a brief shift to moderate southwesterlies as more clouds roll in on Wednesday afternoon.

Avalanche Summary

No new avalanches reported.

Snowpack Summary

A thick supportive crust has frozen on the surface at lower elevations, with a trace amount of fresh snow on top in some places. The late January crust and surface hoar is down about 30-50 cm and recently failed with moderate effort in snowpack tests, but the failure displayed very little propensity for propagation. The mid-December buried crust layer is down about 50 cm at 2150 metres elevation and continues to react to hard forces in tests with stubborn results. The snowpack was moist down to the ground on Saturday, and is expected to re-freeze with forecast overnight temperatures. There is not much snow below 1600 metres, and a lot of bare areas below 1200 metres.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.