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Avalanche Forecast

Archived

Mar 31st, 2021–Apr 1st, 2021

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

Regions

Purcells.

A forecast uptick in southwest winds should sustain wind slab problems at high elevations. Stay aware of cornices that formed fragile new growth during the storm.

Confidence

Moderate -

Weather Forecast

Wednesday night: Clear. Moderate to strong southwest winds increasing into the morning.

Thursday: A mix of sun and cloud with possible isolated flurries. Moderate to strong southwest winds. Alpine high temperatures around 0 with freezing levels to 2000 metres.

Friday: A mix of sun and cloud with isolated flurries. Light southwest winds. Alpine high temperatures around -1 with freezing levels to 1900 metres.

Saturday: Mainly sunny. Light southwest winds. Alpine high temperatures around +2 with freezing levels to 2200 metres.

Avalanche Summary

On Monday, numerous skier and explosive triggered storm slab avalanches were reported size 1-1.5, largely on NW aspects. By Tuesday, storm slabs became more stubborn to explosives and results were limited. Observations in the Hellroaring area, which received less snow, include a few size 1 wind slabs and a cornice-triggered size 1.5.

Reports during the storm on Sunday include several natural storm slabs size 1-2 and a natural size 2 loose wet avalanche on a northeast aspect around 1700 m. It is suspected to have scrubbed down to a crust near the ground, as rain and warm temperatures destabilized the full depth of the snowpack.

Snowpack Summary

New surface crusts have likely formed on solar aspects and below about 2000 metres. Forecast isolated flurries may add a skiff of dry snow to higher elevations while crusty surfaces below treeline become moist with daily rising freezing levels or light rain.

15-40 cm of recent snow has otherwise seen some redistribution by southwest to northwest wind, and seems to be bonding well with underlying surfaces.

A widespread crust layer from the mid-March warm spell can be found 30-60 cm deep, and small surface hoar has been observed at this depth on some isolated north-facing slopes. Reports suggest the snow is generally well bonded to these layers. Deeper layers are strong and have been unreactive over the past few weeks. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Remember that in the spring strong solar radiation and warm temperatures can weaken the snow in a matter of minutes.
  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.

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.