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Avalanche Forecast

Archived

Nov 22nd, 2013–Nov 23rd, 2013

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

Regions

Purcells.

Forecasts are based on limited observations. You need to be the detective. Dig down, test weak layers and keep an eye on rising temperatures throughout the weekend.

Confidence

Poor - Due to the number of field observations

Weather Forecast

High pressure will dominate though the forecast period. This will bring warming temperatures, rising freezing levels and temperature inversions. Some forecasts suggest alpine temperatures could rise as high as 5 degrees celsius. Ridgetop winds will be light from the West and no significant precipitation is expected.

Avalanche Summary

Earlier this week a widespread avalanche cycle occurred from all aspects up to size 3.5, failing on the early season crust. Recently, slab avalanches up to size 2 have been easily rider triggered and some have failed in depth hoar at the base of the snowpack.

Snowpack Summary

The average snowpack depths at upper elevations are near a metre or more. The recent storm snow seems to be settling, but wind slab problems do exist. A bigger concern deeper in the snowpack is a melt-freeze / rain crust that formed early October. This is generally found from 70-150 cm down, with facetted (sugary) crystals above and below that are bonded poorly. The crust seems to be widespread through the region, however on northerly aspects it may be more predominant and allow for wider propagations and bigger avalanches, especially in places that have smooth ground cover (glacier ice, grassy slopes, rock slabs etc.).The snowpack is still young, thin and highly variable.

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.

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.