Avalanche Forecast

Archived

Jan 28th, 2018–Jan 29th, 2018

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 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

Purcells.

Significant uncertainty exists with forecast snowfall amounts: If you see more than 30 cm of new snow consider the danger to be HIGH and avoid all avalanche terrain, including overhead hazard.

Confidence

Low - Forecast snowfall amounts are uncertain

Weather Forecast

Monday: 10 cm snow Sunday overnight into Monday with another 10-20 cm snow during the day. Moderate to strong south-westerly winds. Alpine temperature near -2.Tuesday: 5-10 cm snow. Light to moderate south-westerly winds. Alpine temperature near -5. Wednesday: Cloudy with isolated flurries. Light south-westerly winds. Alpine temperature near -5.More information can be found in the Mountain Weather Forecast.

Avalanche Summary

On Saturday near Kimberley, skiers remote-triggered two Size 2 avalanches, by a convex roll near 2000m elevation. Crown height was 60-70cm, suggesting the snow ran on the mid January layer. See the MIN report for more details. On Friday we received reports of several explosives-triggered persistent slab avalanches (to Size 3), primarily on northerly aspects above 2200m, running on the Jan 5th surface hoar layer. With consistent loading over the next two days, human triggering will remain likely and avalanches could be surprisingly large due to the structure of the snowpack.

Snowpack Summary

The current snowpack is complex, with three active weak layers that we are monitoring.1) 50-80 cm of recent storm snow overlies a crust and/or surface hoar layer (from mid-January). The crust is reportedly widespread, except for possibly at high elevations on north aspects. The surface hoar is 10 to 30 mm in size, at all elevation bands. The recent snow fell with strong south winds, producing wind slabs and cornices in lee features. 2) Deeper in the snowpack (down 60-90 cm), a persistent weak layer known as the early-January layer is present at all elevation bands, and composed of surface hoar on sheltered slopes and sun crust on steep solar aspects. Recent snowpack tests have shown sudden fracture characters with moderate loads and high propagation potential. 3) Another persistent weak layer that was buried mid-December is 70 to 110 cm deep and consists of a facet/surface hoar/crust combination. It is most problematic at and below tree line.A rain crust buried in November is 100 to 150 cm deep and is likely dormant for the time being.

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.