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Avalanche Forecast

Archived

Feb 5th, 2013–Feb 6th, 2013

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

South Coast.

Confidence

Good

Weather Forecast

Wednesday: Expect cloudy skies with flurries and strong southwesterly winds with alpine temperatures reaching -7. 5-15cm are possible.Thursday: Continuing cloudy, with a chance of lingering flurries. Winds should turn more northerly and ease to light values with alpine temperatures reaching -5.Friday: Mixed skies with continued light northerly winds and temperatures around -3.

Avalanche Summary

Isolated windslab events have been reported from alpine lee zones.  As the storm snow deepens, expect the avalanche activity to pick up.

Snowpack Summary

Between 15-25cm of new snow has fallen in the past 36hrs. Consistent southwesterly winds have redistributed this into fresh windslabs on lee terrain features in the alpine and at treeline. Freezing levels have crept up higher than expected yielding moist surface snow up to 1600m in some locations. A new surface crust below treeline will be the outcome of this warming.The newly buried surfaces are old wind slabs (behind ridges, ribs and on lee slopes) and sun crusts on south and west facing slopes. Down a further 20-50 cm sits a persistent interface comprising of crusts, facets and surface hoar crystals. Recently, this layer has been reactive only in sheltered areas at and below treeline where the surface hoar lingers. The mid pack is generally well settled.

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.