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Avalanche Forecast

Archived

Mar 25th, 2021–Mar 26th, 2021

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

Regions

Sea To Sky.

Lingering wind slabs in open terrain at upper elevations are the main concern.

Confidence

High - The snowpack structure is generally well understood.

Weather Forecast

THURSDAY Night: Cloudy with clear periods, light northeast wind, treeline temperatures around -6 C, freezing level 1000 m.

FRIDAY: Mix of sun and cloud, light northwest wind, treeline temperatures around -4 C, freezing level 1400 m.

SATURDAY: Mainly cloudy with sunny breaks, moderate southwest wind, treeline temperature around -3 C, freezing level 1400 m.

SUNDAY: Snow, moderate to strong southwest wind, treeline temperatures around -6 C, freezing level 1100 m.

Avalanche Summary

A few cornices were triggered naturally and from explosives on Tuesday and Wednesday. They were very large, as is expected at this time of year.

Looking forward, wind slabs and cornices may remain triggerable at higher elevations and use caution on sun-exposed slopes if clear skies prevail.

Snowpack Summary

Around 5 to 10 cm of snow accumulated Tuesday night, with strong wind from the southwest switching to northeast. New wind slabs likely formed during this time, which may linger in steep, alpine terrain features. This snow adds to the 30+ cm that accumulated on the weekend. All of the new snow sits above a widespread crust, with the exception of high north-facing terrain. Observations suggest the snow has bonded well to these old interfaces. There are currently no concerning weak layers in the snowpack, although a spotty early season facet layer deep in the snowpack could return as a problem later in the season.

Remember that cornices along ridgelines are large at this time of year and always have the possibility of failing naturally or from the weight of a human.

Terrain and Travel

  • Carefully evaluate steep lines for wind slabs.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.