Avalanche Forecast

Archived

Nov 25th, 2018–Nov 26th, 2018

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, human triggered possible.

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

Purcells.

A warm and wet system is moving across the province. Slabs will gain strength with increased winds and rising temperatures. In areas with higher than forecasted snowfall, avalanche hazard may be higher than forecasted.

Confidence

Low - Intensity of incoming weather systems is uncertain

Weather Forecast

SUNDAY NIGHT: Mainly cloudy with isolated flurries / Precipitation: up to 5 cm / Light south ridge windMONDAY: Cloudy with flurries / Accumulation: 5-10 cm / Alpine temperature: High 0C / Moderate south ridge wind / Freezing level 1500mTUESDAY: Cloudy with flurries / Accumulation: up to 10 cm / Alpine temperature: High +2C / Moderate south-southwest ridge wind / Freezing level 1700mWEDNESDAY: Cloudy with flurries / Accumulation: up to 5 cm / Alpine temperature: High -3 / Light to moderate southwest ridge wind / Freezing level 1500m

Avalanche Summary

On Saturday, a large human triggered avalanche was reported in the South Columbia forecast region. The size 3 avalanche occurred on a steep, north aspect in the alpine and failed to ground, likely on the October crust. Find the MIN report here.Small windslabs have been triggered by skiers and explosives in cross-loaded and lee terrain features at treeline and alpine elevations. Earlier in the month, a natural avalanche cycle took place over the late October crust/facet combination. Be aware of the continued possibility for smaller avalanches to 'step down' or even initiate at this deeper layer.

Snowpack Summary

15-30 cm recent snow has buried a surface hoar/sun crust layer. Reports in the region show this variable layer sitting above a layer of recently reactive wind slab. This wind slab layer overlies yet another widespread layer of surface hoar from mid-November, now found about 20-40 cm deep. A final, prominent feature of the snowpack is a combination of a melt-freeze crust and underlying sugary, faceted snow found around the base of the snowpack. Avalanches have been triggered where there is a slab above this crust.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.