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Avalanche Forecast

Archived

Apr 13th, 2022–Apr 14th, 2022

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

Regions

Yukon.

Carefully assess your line for wind slab hazard. Remember that small avalanches can have large consequences in the wrong terrain.

Cornices are large and exposure to them should be minimized, especially during warm or sunny weather.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

WEDNESDAY NIGHT: Clear skies, no precipitation. 20-40 km/h wind from the northeast, treeline temperatures drop to -15 C.

THURSDAY: Mainly clear skies, high cloud building into the afternoon. No precipitation, light wind from the north, treeline temperatures reach -8 C.

FRIDAY: Cloudy with light flurries. 10-25 km/h wind from the west, treeline temperatures around -10 C.

SATURDAY: Cloudy with flurries, up to 5 cm of accumulation. 15-30 km/h wind from the southwest, treeline temperatures around -8 C.

Avalanche Summary

A very large cornice-triggered wind slab avalanche (size 3) was observed near White Pass on Tuesday. This avalanche occurred on an east aspect in the alpine.

Several small human-triggered wind slabs (size 1) were reported during the outflow wind event on Monday and Tuesday. A few other large cornice failures were observed on Sunday.

This MIN report from Tuesday paints an excellent picture of the lingering wind slab problem and conditions in the White Pass area.

Snowpack Summary

Strong northerly wind has affected most surfaces and left hard wind slabs in alpine terrain. Sun crusts are found up to 1400 m on south and west-facing slopes, while surfaces on other aspects are dry. The mid-snowpack is generally strong, overlying weak basal facets at the base of the snowpack. 

Terrain and Travel

  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Avoid exposure to slopes that have cornices overhead.
  • Cornices often break further back than expected; give them a wide berth when traveling on ridgetops.

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.