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Avalanche Forecast

Archived

Mar 6th, 2017–Mar 7th, 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.

We are surprised by the size of the avalanches that occurred from avalanche control on Sunday and Monday - up to 400m propagations! Unsure about the snow depths on Mt. Dennis, so ice climbers be wary of the overhead hazard right now.

Weather Forecast

Overcast skies with light precipitation for Tuesday, but no measurable accumulation expected. Temperatures will remain cool, ranging from -12 to -18 and expect winds straight out of the west at about 30-40 km/hr in alpine areas. A bit more snow expected for Wednesday.

Snowpack Summary

40cm of storm snow has developed into a touchy storm slab that is very sensitive to triggers 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

Avalanche control on Mt. Bosworth today (near Lake O'Hara) resulted in widespread fracture propagations (up to 400m)that released very easily. The ease and speed of the fractures was surprising; 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.

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.