Avalanche Forecast

Archived

Feb 27th, 2016–Feb 28th, 2016

Alpine

Natural avalanches unlikely, human triggered possible.

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.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Columbia.

Forecast snowfall and wind on Sunday could build fresh and touchy wind slabs in exposed terrain. Choose your lines carefully and avoid exposure to terrain traps.

Confidence

Moderate

Weather Forecast

Sunday: Cloudy with light snow 5-10 cm. The freezing level is around 1400-1500 m. Ridge winds are moderate from the S-SW. Monday: Up to 10 cm overnight then cloudy with sunny breaks and a chance of flurries. The freezing level rises to 1200-1400 m during the day. Ridge winds are light. Tuesday: A mix of sun and cloud. The freezing level jumps up to 1500 m and winds remain light.

Avalanche Summary

Avalanche activity on Friday mainly consisted of loose wet or dry sluffs (depending on aspect) and natural cornice falls. There was also a few reports of natural and skier-triggered wind slabs up to size 1.5 in exposed north-facing terrain. On Thursday, natural and skier-triggered persistent slab avalanches were reported as well as large natural cornice releases and loose sluffing up to 2.5 on solar aspects. A skier triggered a size 2 slab on a northeast aspect convexity at 2150m which released on the February 21 surface hoar layer down 40cm. Two size 1 soft slab avalanches were reported from a northwest aspect which released down 20cm on a layer of surface hoar (buried Feb. 21). A couple natural cornice falls also triggered size 3 persistent slabs on north-facing slopes in the alpine.

Snowpack Summary

Up to 10 cm of new snow sits on a sun crust on solar aspects and surface hoar on shady and sheltered slopes. This new snow may have undergone a melt-freeze cycle on solar aspects on Saturday. New wind slabs are expected to form over the weekend with forecast moderate southwest winds in the alpine. A weak layer of surface hoar and/or a sun crust buried February 21 can be found 15-60cm below the surface. This layer is reported to be increasing in reactivity in the deeper snowfall areas as the week old storm snow continues to settle into a cohesive slab with recent warm temperatures. The surface hoar and/or crust layer which was buried February 10 is now down 60-100cm and has been responsible for some very large avalanches recently. This layer is expected to become much less reactive over the weekend with cooling temperatures. Large cornices have recently been a concern but should also gain strength will colder temperatures.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.