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Avalanche Forecast

Archived

Dec 31st, 2018–Jan 2nd, 2019

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

Regions

Vancouver Island.

Main concerns: Wind Slab, Cornice Fall.

Travel & Terrain Advice

Past warm and wet conditions, followed by a rapid drop in freezing level and temperatures have rapidly changed the snow surface. Expect a supportive crust to be smooth and slippery. Ensure appropriate self arrest equipment when traveling in terrain and be cognizant of your location in terrain. Focus on an emphasis on terrain trap avoidance, example: sliding over steep terrain and cliffs.

Avalanche Summary

Numerous Loose Wet avalanches observed and reported over the previous forecast period.

Snowpack Summary

Warm and wet conditions followed by a cooling period have promoted the development of an upper rain crust. This rain crust is supportive to both foot and ski penetration. Above 1600 meters suspected wind slab development has occurred with precipitation amounts in excess of 50 cm and strong south westerly winds. Due to the warm temperatures, these upper snow pack instabilities are likely to be present but becoming less likely to human triggering. A crust can be found in the mid snow pack, buried around December 22nd and is currently non reactive. Below this a well settled and uniform snow pack is present.

Snowpack Details

Surface: A supportive rain crust all aspects and elevations. Upper: moist and settling. Mid: A crust buried Dec 22 exists down up to 40 cm dependent elevation. Lower: well settled.

Past Weather

A powerful westerly flow pushed past to the south of the forecast area. Warm and wet conditions prevailed, with up-to 60mm of precipitation in westerns zones and the entire region seeing freezing levels rise to 1400 meters. The warm temperatures failed to linger and quit earlier than expected. In the wake of the storm a moderately strong ridge of high pressure flooded the region with cooling temperatures and clear sky.

Weather Forecast

A ridge of high pressure is scheduled to remain in the region until next year keeping the sky clear and temperatures and freezing levels low. Late Tuesday night the ridge is forecast to resign. Following this expect another wave of precipitation mid day Wednesday accompanied by warming temperatures and strong south west wind.

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.