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Avalanche Forecast

Archived

Jan 30th, 2018–Jan 31st, 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

Purcells.

Conditions remain primed for human-triggered avalanches. Give the snowpack time to settle before pushing into more aggressive terrain.

Confidence

Low - Due to the number and quality of field observations

Weather Forecast

Wednesday: Cloudy with isolated flurries. Light westerly winds. Alpine temperature near -10.Thursday: Occasional flurries (2-5 cm possible). Moderate south-westerly winds. Alpine temperature near -8.Friday: 5-10 cm snow. Light to moderate south-westerly winds. Alpine temperature near -6. More information can be found in the Mountain Weather Forecast.

Avalanche Summary

A widespread natural avalanche cycle to Size 3.5 was reported on Tuesday, with larger and more frequent avalanches in the north of the region where storm snow totals were higher. 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. Conditions remain primed for human triggered avalanches, with the potential for some surprisingly large avalanches due to the structure of the snowpack.

Snowpack Summary

Large differences in storm snow totals were observed in the region on Monday into Tuesday: values ranged from 2 to 32cm!!! Overnight winds were strong to extreme from the south west and temperatures spiked to -3 at tree line. The current snowpack is complex, with three active weak layers that we are monitoring:1) 60-100 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 70-100 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 80 to 120 cm deep and consists of a facet/surface hoar/crust combination. It is most problematic at and below tree line.

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.