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Avalanche Forecast

Archived

Mar 7th, 2017–Mar 8th, 2017

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.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Little Yoho.

Storm slab's continue to be reactive throughout the forecast region. Large avalanches and remote triggering were observed today on this layer.

Weather Forecast

A small pulse tonight bringing 5-10cm of snow and moderate winds, Wednesday will be a mix of sun and cloud with temperatures staying below freezing. Expect short convective storms through the week with heavy precipe at times.

Snowpack Summary

40-50cm of storm snow has developed into a touchy storm slab that are sensitive to trigger at treeline and above. This sits over a supportive mid-pack, with the lower half of the snowpack consisting of weak facets and depth hoar. There is isolated wind effect near ridge crests only; the notable observation is the lack of wind effect.

Avalanche Summary

Recent avalanche control on Mt. Bosworth resulted in widespread fracture propagations (up to 400m) that released very easily. Most avalanches occurred in the recent storm snow and one size 3 released on the Dec 19 facets. Lots of storm slab avalanches observed in the backcountry. More avalanche control today showed similar results on HWY 93S.

Confidence

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.