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Avalanche Forecast

Archived

Jan 26th, 2018–Jan 27th, 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 possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

South Rockies.

New snow and wind are adding to a snowpack with several buried weak layers. Best to stick to conservative terrain, avoid wind-loaded areas, and back off if you see classic warming signs like whumpfing or cracking.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

TONIGHT: Cloudy with clear periods. Ridge wind moderate, southwest. Temperature -12. Freezing level valley bottom.SATURDAY: Cloudy, flurries. Accumulation 1-6 cm. Ridge wind light to moderate, south. Temperature -6. Freezing level valley bottom.SUNDAY: Cloudy, light flurries. Accumulation trace. Ridge wind light, southwest. Temperature -6. Freezing level valley bottom. MONDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind strong, southwest. Temperature +1. Freezing level rising to 1900 m. 

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 treelineand 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.A 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.