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Avalanche Forecast

Archived

Feb 8th, 2017–Feb 9th, 2017

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Rockies.

A Special Public Avalanche Warning Applies for this Region.Additional new snow combined with warmer temperatures and wind on Thursday will give a rise to avalanche activity. Forecast snow amounts vary throughout the region.

Confidence

Moderate - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

THURSDAY: Periods of snow, accumulation 15-35cm with the greater amounts in the southernmost portions of the region / Moderate to strong southwest winds / Alpine temperature -2 with a freezing level of 1500mFRIDAY: Cloudy with isolated flurries / Moderate to strong west wind / Alpine temperature -4 with a freezing level of 1200mSATURDAY: Cloudy with sunny periods / Moderate west wind / Alpine temperature -9More details can be found on the Mountain Weather Forecast.

Avalanche Summary

With additional snow, warming temperatures and wind on Thursday expect to see another spike in avalanche activity as the load grows over weak layers deeper in the snowpack. Storm slab avalanches have the potential to step down to the basal weakness which would drastically increase the size and destructive potential of a resulting avalanche. On Monday, numerous skier triggered storm slab avalanches size 1-1.5 were reported. Explosives also triggered storm slabs up to size 2.5. These slabs were typically around 30 cm thick. One of these storm slab avalanches stepped down to the basal weakness resulting in a slab that was up to 150 cm thick. On Monday in the Lizard region, natural avalanches up to size 2.5 were observed.

Snowpack Summary

Another 20-30cm of new snow is expected through the day Thursday to add to 90 cm of new low density storm snow that accumulated last weekend. Strong shifting winds have redistributed the previous storm's snow in exposed terrain forming touchy wind slabs. These wind slabs are now obscured by the latest blanket of snow. All this overlies a highly variable old surface which may include wind affected surfaces, facets, and/or a rain crust below around 1500 m. Recent reports suggest a poor bond between the storms' snow and the old surface. In deeper areas, the snowpack appears to be well settled with isolated concerns about the mid-December facet layer which was buried 50-100 cm deep prior to the weekend storm. In shallow snowpack areas and at lower elevations, the snowpack is weak, faceted, and has no structure. Prior to the storm, it was possible to step onto the snow surface in these areas and sink right to the ground.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.