Avalanche Forecast

Archived

Mar 31st, 2012–Apr 1st, 2012

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

South Coast.

Confidence

Fair - Intensity of incoming weather is uncertain on Monday

Weather Forecast

Sunday: a mix of sun and cloud with light snowfall - moderate southwest winds - freezing level at 950m Monday: heavy snowfall continuing overnight - strong to extreme southwest winds - freezing level between 1000 and 1500m Tuesday: light snowfall with possible clearing - moderate southwest winds - freezing level at 700m

Avalanche Summary

Numerous natural and human-triggered slabs to size 2.5 were observed in the Duffey lake area over the last few days. The suspected sliding layer has consistently been the March 26th interface. On Face Mountain in the Railroad Pass area 2 sledders triggered a size 2 avalanche while riding the slope at the same time. The slide was 60m wide and 50cm deep and was most likely triggered on the March 26 layer. The sledders escaped without injury.

Snowpack Summary

40-60cm of new snow now overlies an interface that was buried on March 26. This interface consists of a crust that exists on all aspects and elevations except north facing slopes at treeline and above where small surface hoar (5mm) may be found in sheltered areas. This week's snowfall has been accompanied by consistently moderate and at times gusty southerly winds forming windslabs in lee locations. The bonds between the new snow and this buried interface have been weak, especially in locations where the surface hoar is present. Easy planar results have been observed in testing at treeline on surface hoar size 2-4mm. At lower elevations, the consistent high freezing levels have kept the new snow moist and heavy. The deep, persistent early February layers linger in the snowpack and remain a concern with heavy triggers and rapid loading. Cornices are huge, and have continued to grow with this weather pattern.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.