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Avalanche Forecast

Archived

Feb 25th, 2013–Feb 26th, 2013

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

Regions

South Columbia.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Tuesday: Light snowfall / Light northwest wind / Freezing level at 900mWednesday: Light snowfall/ Light west winds / Freezing level at 900mThursday: Light to locally moderate snowfall/  Moderate south winds / Freezing level at 800m

Avalanche Summary

On Sunday a skier remotely triggered a size 2 slab avalanche from 40 metres away. The avalanche, which occurred on a north aspect at 2000m, failed on the February 12 surface hoar. On Monday numerous deep size 2 avalanches were triggered off small rolls in a popular sledding area. These avalanches were also triggered on the February 12th surface hoar. These events speak to the touchy nature of the persistent avalanche problem. I would expect human triggering at this deep persistent interface to be a very real possibility throughout the week.

Snowpack Summary

Moderate to locally heavy snowfall on Sunday adds to ongoing potent storm instabilities which seem to be most reactive as a wind slab in exposed terrain or as loose snow in more sheltered areas. A weak surface hoar layer which was buried on February 12th now exists up to a metre below the surface in many places. The touchy and destructive nature of this persistent weakness remains a primary concern for professionals in the region. This interface has also shown reactivity on southerly aspects where a sun crust also exists. The mid to lower snowpack are generally strong and well settled. I anticipate significant cornice growth with the current weather pattern, and expect them to be weak and potentially destructive.

Problems

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.

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.