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Avalanche Forecast

Archived

Feb 27th, 2013–Feb 28th, 2013

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

Regions

Purcells.

Confidence

Poor - Timing, track, or intensity of incoming weather is uncertain on Friday

Weather Forecast

Thursday: Overcast with sunny breaks and little to no precipitation during the day. Winds light-moderate from the southwest and alpine temperatures of -5. Freezing level rising to 1400m.Friday: Thursday night into Friday a warm front associated with a Pineapple Express weather system will affect the region. Unseasonably warm temperatures, strong southwesterly winds are forecast. Depending on the how the system tracks across the province, locally heavy precipitation is possible. Freezing level 1900mSaturday: Light precipitation, winds light southwest and freezing level of 1700m.

Avalanche Summary

Recent reports indicate skier controlled and remote loose and slab avalanches to size 1.5 in the alpine and upper end of tree-line.

Snowpack Summary

The recent new snow has been redistributed by the wind and is possibly reactive as a wind slab in exposed terrain or as loose snow in sheltered areas. The variably reactive February 12th and 15th surface hoar layers now exist up to 80cm below the surface and seem most prevalent on the west side of the region. This interface may also be reactive on solar aspects where a sun crust exists. A surface hoar layer buried on February 23 is still on the radar of some operators. This layer has been less likely to trigger by skiers, but may still be sensitive to large loads like avalanches in motion or cornice fall. The mid and lower snowpack are generally well settled and strong.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.