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Avalanche Forecast

Archived

Mar 22nd, 2021–Mar 23rd, 2021

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.

Assess you line for wind slabs before committing to steep terrain. Convex slopes below ridge tops are the most likely places to trigger slabs. 

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

MONDAY NIGHT: Partly cloudy. Light west-northwest wind, alpine low -12C, and freezing level valley bottom.

TUESDAY: Sunny breaks with patchy clouds through the day. Light to moderate northwest wind, alpine high -4C, and freezing level rising to 1500 m.

WEDNESDAY: Cloudy with flurries, 5 cm. Light southwest wind, alpine high -3C, and freezing level rising to 1500 m.

THURSDAY: Unsettled with flurries, 5 cm. Light west wind, alpine high 0C, and freezing level rising above 1500 m.

Avalanche Summary

On Sunday, dry loose avalanches failed naturally and were reactive to skiers with fresh low density snow sliding on crusts or compact surfaces.

On Saturday, several natural size 1.5 wind slabs were observed on northeasterly aspects in the alpine. Size 2 slab avalanches were reported failing naturally on steep, south slopes (MIN report and deeper snowpack here). Sluffing and dry-loose avalanches were reported in steep terrain.

A few small loose wet avalanches were reported Wednesday through Friday on solar aspects into the alpine. A small wind slab was also reported from a high elevation east facing aspect last Thursday.

Snowpack Summary

South-southwesterly winds have impacted loose snow developing slabs in immediate lees. 5-15 cm fresh snow covers dry settled snow on northerly aspects above 1800m, and crusts on solar aspects and lower elevations. Loose snow is sluffing easily on the crust. Large cornices loom over alpine ridgetops. Below 1300 m, the snowpack is moist.

A persistent weak layer of facets 40-60 cm deep that was buried in mid-February was reactive in the north of the region earlier this month but since the first week of March, only a couple of avalanches have been reported on this layer resulting from large triggers such as cornice fall. There are several other weak layers deeper in the snowpack composed of old surface hoar, facets and/or crusts, all of which have been recently unreactive.

Terrain and Travel

  • Be alert to conditions that change with elevation, aspect and exposure to wind.
  • Carefully evaluate steep lines for wind slabs.
  • Minimize your exposure time below cornices.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

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.