Avalanche Forecast

Archived

Feb 12th, 2012–Feb 13th, 2012

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, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

Purcells.

Confidence

-1 - -1

Weather Forecast

A weak Pacific system is expected to run into the ridge of high pressure on Monday afternoon that should cause some light flurries. Clearing skies are expected by early evening. The wind should change to north by Tuesday morning as more high pressure moves across the interior. Some remaining moisture may cause a brief period of flurries in the morning. Clear skies and strong solar radiation is expected during the afternoon on Tuesday, however northwest winds should help to keep alpine maximum temperatures close to -10.0 on shaded aspects. Temperatures should drop down to about -15.0 in the alpine by Wednesday morning. The ridge of high pressure is expected to continue to bring clear skies and light winds during the day Wednesday. Alpine temperatures may rise above freezing on solar aspects, but should remain slightly below freezing on shaded aspects.

Avalanche Summary

No reports of new avalanches.

Snowpack Summary

Widespread surface hoar has been buried by a trace of new snow in most of the region. A melt-freeze crust has developed on southerly aspects at all elevations. North and east aspects continue to have dry snow and some surface hoar sloughing in steep terrain. The January 13th surface hoar layer is buried about 40 cm below the surface, and may still be reactive in thinner snowpack areas. Basal facets have not been reactive, but operators continue to monitor this layer in tests. Triggering this deep persistent weak layer is unlikely, but shallow snowpack areas or shallow weak areas adjacent to deeper wind loaded slopes are suspect locations.

Problems

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.