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Avalanche Forecast

Archived

Dec 16th, 2011–Dec 17th, 2011

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

Regions

Northwest Inland.

Confidence

Fair - Freezing levels are uncertain on Saturday

Weather Forecast

Between friday night and saturday morning 10-20cm of snow and moderate to strong southwest winds are forecast for the region. Freezing levels for this period are expected to rise to 1500m with a possibility of freezing rain at lower elevations.A clearing trend is forecast for saturday afternoon and into sunday morning as winds eventually switch to light and northerly and freezing levels fall to surface.The clearing will be short-lived as more heavy snowfall and strong southwest winds will resume on sunday afternoon and into monday. Freezing levels on monday to sit at about 800m.

Avalanche Summary

Several size 2 natural avalanches were reported earlier in the week. These occurred on northerly aspects failing on the SH/CR/FC combo layer. I suspect we will see a natural cycle through the early part of the weekend with more snow and wind forecast.

Snowpack Summary

A few centimetres of new snow and surface hoar crystals are sitting on the less recent 20cm of storm snow which fell earlier in the week. This storm snow we received earlier this week sits on a variety of old weak snow surfaces including surface hoar, melt-freeze crusts and facetted snow. For the most part all aspects between 900m-2000m have a hard melt freeze crust. This crust is widespread and is lingering in most start zones. This is the layer of concern as we receive more snow and wind Friday and Saturday. Above this crust surface hoar (feathery crystals) and facets (sugary crystals) may be preserved. This exists at treeline and below treeline elevations. The recent winds in the alpine seem to have destroyed the surface hoar in exposed areas eliminating that problem but creating a wind slab problem. These wind slabs are in the immediate lee of features, sitting on the SH/CR/FC combo. They are reactive and rider triggered avalanches are likely. The midpack seems to be well settled and strong. Thanks to those who have sent in field observations. If you have any info from the field, we would love to hear from you. Write to us at [email protected]

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.

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.