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Avalanche Forecast

Archived

Dec 18th, 2011–Dec 19th, 2011

Alpine
Natural and human triggered avalanches likely.
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

Northwest Inland.

Confidence

Poor - Intensity of incoming weather is uncertain on Monday

Weather Forecast

Snowfall amounts for monday are highly uncertain, but some models are calling for 20-30cm on the west side of the region. Expect moderate to strong wind values and freezing levels between 500-1000m.On tuesday expect light to moderate snowfall with light westerly winds in the morning with clearing late in the day. Forecast freezing levels at about 300m.Clearing is forecast for wednesday with light to moderate southwest winds and freezing levels at surface.

Avalanche Summary

On saturday evidence of a size 2 natural avalanche cycle was reported in the Hankin area. There was also human triggering to size 2.5 in the same area. It is thought that these slides are releasing on the crust/surface hoar/facet interface. Forecast weather is uncertain for monday. If precip values are on the high side, expect another spike in natural avalanche activity for the region.Any information (professional or recreational) from the field is highly appreciated. Please send your observations to [email protected].

Snowpack Summary

Over the past week the region has received approximately 40cm of snow that now sits on a variety of weak snow surfaces (melt-freeze crust, surface hoar above the crust and facetted snow below the crust) that are a result of rain and then the early December dry spell. This crust is widespread and is lingering in most start zones up to 2000m. The recent winds in the alpine seem to have destroyed the surface hoar in exposed areas in the alpine possibly eliminating that issue, but creating a wind slab problem. In short, the upper snowpack is variable and showing easy shears in test results. A cautious approach is required as monday's forecast calls for new slabs to continue to form over the buried weak layers. The midpack seems to be 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.

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.