Avalanche Forecast

Archived

Jan 28th, 2018–Jan 29th, 2018

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

South Rockies.

With several buried weak layers and a rising freezing level on Monday, the snowpack is primed for human triggering. A conservative approach to terrain selection is recommended.

Confidence

Moderate - Freezing levels are uncertain on Monday

Weather Forecast

MONDAY: Cloudy with flurries, accumulation 5-10cm / Strong southwest wind / Alpine temperature -2 / Freezing level 1800mTUESDAY: Flurries, accumulation 5cm / Strong west wind / Alpine temperature -4WEDNESDAY: Mix of sun and cloud / Light west wind / Alpine temperature -10

Avalanche Summary

On Thursday explosive control work in the Castle area triggered a Size 3 avalanche from a shallow area that propagated and failed on the late-November layer deep in the snowpack. While in the Bull River area a natural Size 1.5 wind slab avalanche was observed on a northwest aspect at treeline and a natural Size 2 in a west-facing cutblock at 1600 m was reported to have failed on the mid-December layer.The snowpack in the region remains suspect with several buried weak layers displaying classic signs of instability such as whumpfing and cracking. The recent video posted to the Avalanche Canada South Rockies field team Facebook page paints a pretty clear picture. https://www.facebook.com/avcansouthrockies/videos/1894352117306941/.

Snowpack Summary

Amounts vary across the region however, about 20-50 cm of recent storm snow now covers both a new layer of feathery surface hoar in sheltered areas as well as sun crust on solar aspects buried mid-January, and about 30-60 cm below the surfaces lies the early-January surface hoar layer.About 60-80 cm below the surface a weak layer of feathery surface hoar crystals and/or sun crust buried mid-December is found at treeline and below treeline elevations. Near the base of the snowpack the weak early-season layer of rain crust and sugary facets buried late-November exists. Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread. Snowpack depths are also variable across the region and typically thinner in northern areas than in areas to the south.

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.

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.