Avalanche Forecast

Archived

Mar 17th, 2012–Mar 18th, 2012

Alpine

Natural avalanches possible, human triggered probable.

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.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Kananaskis.

20cm of new snow overnight on Friday/Saturday. Conditions are improving but this is not the time to push into bigger terrain. Conservative routes and decision making is essential at this time.

Confidence

Good

Weather Forecast

No new snow expected over the next 24hrs. Winds are forecast to be light out of the south and temperatures around -8C at treeline during the middle of the day. Cloudy conditions will persist and visibility into alpine areas will be limited.

Avalanche Summary

1 size 3 Na on a steep (40-45deg) NE aspect at 2800 near Black Prince. 300m wide, up to 1.5m deep failing in the storm snow layers, as well as stepping down to the Valentines day crust as well as ground in some of the steeper rocky areas. 1 size 3 Na on a N aspect on the Rundle bowls above the Canmore Nordic Center. Slide ran full path, stopping at the end of its historical trim lines. No other information available on this due to limited visibility. 2 other size 2 avalanches were also observed on N and E aspects at 2600m. Both of these slides occurred in steeper unsupported terrain failing within the storm snow and stepping down to the Valentines day interface.

Snowpack Summary

An additional 20cm of new snow fell overnight. Over the past 72hrs, up to 50cm of new snow has fallen under the influence of a light to moderate SW flow. The Valentines day surface hoar layer is now buried down up to 160cm and is becoming more stubborn to trigger. Propagation saw tests are showing that if this layer is triggered it will propagate across a terrain feature but it is becoming less reactive to light loads such as a skier. On solar aspects the March 10th temperature crust is down 50-60cm on solar aspects. A thin layer of weak facetted crystals is developing on top of this crust and the bond between the new snow and the underlying crust should be carefully evaluated. Any avalanche initiated in the upper snowpack will likely step down to the Valentines day interface so skiers should keep this on their mind as they travel.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.

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.