Avalanche Forecast

Archived

Nov 27th, 2015–Nov 28th, 2015

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Regions

Purcells.

Rising temperatures in the alpine may change the snowpack dramatically, especially on solar aspects. Forecasters are working with little information this early in the season. Share your observations through the Mountain Information Network. MIN

Confidence

Fair - Due to the number and quality of field observations

Weather Forecast

An arctic high continues to dominate the weather pattern over western Canada and is not forecast to move out of the area until Tuesday or Wednesday next week. In the meantime, an above-freezing layer (AFL) of air will pass through the region between 1500 and 3000m bringing temperatures in that elevation band to as high as +5c., especially on solar aspects. Arctic air pooling in the valley bottoms will keep the temperatures well below freezing until the next storm system flushes out the cold air.

Avalanche Summary

Reports of large avalanches triggered by explosives failing on facts at the base of the snowpack have been received from operators. Surface sluffing of the recent snow in steep terrain has been mentioned as well as a few skier controlled, low density, size 1 avalanches. The general feeling is that these low density size 1's were failing on the Sept. 23rd surface hoar.

Snowpack Summary

The snowpack has been described by local observers as "extremely variable", with wind effect in all open alpine areas from the Northerly winds after the last storm. Surface hoar is widespread and observed to 4mm in sheltered locations, while windward slopes have been scoured down to bare rock in some locations. Cold arctic air and temps down to -20 in some areas have promoting surface facetting. The above-freezing-layer of warm air, now moving through the region could dramatically alter the snowpack. There may be a radical difference in the snowpack depending on the aspect :ie, north or south facing slopes.

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.