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Avalanche Forecast

Archived

Feb 9th, 2017–Feb 10th, 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.

Regions

Purcells.

Conditions are primed for people triggering avalanches, which are expected to be particularly deep and touchy in the southern parts of the region. A Special Avalanche Warning applies to this region. Click here for more details.

Confidence

High -

Weather Forecast

FRIDAY: Cloudy with scattered flurries bringing approximately 5 cm of fresh snow, moderate to strong southwesterly winds, and freezing level around 1400 m.SATURDAY: A mix of sun and cloud, moderate westerly winds, and freezing levels around 1400 m.SUNDAY: Mainly sunny, light but gusty westerly winds and freezing levels rising to 1600 m.

Avalanche Summary

No new avalanches were reported on Wednesday. Reports from Tuesday include numerous explosives-triggered storm slab avalanches up to Size 2.5, with one Size 1 ski cut. Further evidence of numerous recent natural storm slab avalanches up to Size 2 was also reported. Also, a skier accidentally triggered a 50cm thick Size 2 storm slab avalanche on a southwest aspect at 2200 m.Heavy loading from snow and wind is expected to result in continued natural avalanche activity with touchy storm and wind slabs remaining sensitive to light triggers.

Snowpack Summary

15-25cm of fresh snow, accompanied by moderate winds, adds to the 50-100 cm from the past few days, with the heaviest amounts in the southern part of the region. This recent storm snow is forming deep touchy slabs, especially where it has been wind-loaded, which are bonding poorly to the previous snow surface that includes sun crust on steep sun-exposed slopes, faceted snow, as well as surface hoar on sheltered open slopes. Weaknesses are also lingering within the recent storm snow, with 'upside-down' conditions and several easy to moderate shears being reported. A persistent weakness buried mid January is now down 60-120 cm and consists of buried surface hoar in sheltered areas, sun crust on south aspects, and/or faceted old snow. It has generally stabilized but may be sensitive to triggering in isolated areas where surface hoar is preserved. Another surface hoar/facet weakness buried mid-December found 70-140 cm is generally considered dormant. This and deeper persistent weaknesses remain concerns isolated to shallow snowpack areas where they lie closer to the surface.

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.