Avalanche Forecast

Archived

Mar 12th, 2021–Mar 13th, 2021

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Sea To Sky.

Rising freezing levels and sunshine will increase the likelihood of avalanches and cornice failures. Pay close attention to temperatures and minimize exposure to cornices and steep, sun-exposed slopes during the heat of the day.

Confidence

Moderate - Uncertainty is due to difficult to forecast freezing levels.

Weather Forecast

FRIDAY NIGHT - Mainly cloudy / light to moderate southwest wind / alpine low temperature near -1

SATURDAY - Mainly cloudy, clearing in the morning, and then mainly sunny / moderate southwest wind / alpine high temperature near 0 / freezing level 2000 m

SUNDAY - Flurries, 10-15 cm / strong south wind / alpine high temperature near -2 / freezing level 1500 m

MONDAY - A mix of sun and cloud / light variable wind / alpine high temperature near -4 / freezing level 1500 m

Avalanche Summary

Rising freezing levels and sunshine will increase the likelihood of avalanches and cornice failures on Saturday.

On Thursday, there was a report of a human-triggered size 2.5 wind slab avalanche on a southwest aspect at 2300 m, in extreme terrain.

There have been reports most days this week of a few natural and/or human-triggered wind slab and dry loose avalanches, ranging between size 1-2, as well as natural size 1 loose wet avalanches on solar aspects at lower elevations.

Snowpack Summary

Wind slabs can be found on leeward slopes at upper elevations and remain possible to trigger. Solar aspects have a crust on the surface, that may become moist with rising freezing levels and direct sun. Soft, dry snow can be found in sheltered, shaded areas.

Massive cornices exist on ridgelines, which can act as triggers on slopes below.

The mid and lower snowpack is well settled and strong in most areas. A weak layer of facets buried in mid-February may still be found but has been gaining strength.

Terrain and Travel

Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
Minimize exposure to sun-exposed slopes when the solar radiation is strong.
Back off slopes as the surface becomes moist or wet with rising temperatures.
Minimize your exposure time below cornices.

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.

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.