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Avalanche Forecast

Archived

Dec 21st, 2020–Dec 22nd, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
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

Little Yoho.

Avalanche Control is planned for Mt. Stephen, Mt Field and Mt. Dennis on Tuesday December 22. No access to these areas!

Weather Forecast

An early christmas present of 15-20 cm has started to fall as I write this bulletin. This is forecast to fall with mostly light southerly winds which will switch to north and become strong at the tail end of the storm. Tuesday looks cool with clearing skies. Wednesday and Thursday look sunny and cold with lows near -20 and increasing alpine winds

Snowpack Summary

30-60cm over the last week have been redistributed by strong west winds forming windslabs in exposed alpine and treeline areas. The Dec 13 and Dec 7 sun crust/surface hoar/facet layers are down ~ 35cm and ~65cm respectively. The Nov crust/facets sit at the bottom of the snowpack and are generally well bonded. Height of snow at tree line is 80-150cm

Avalanche Summary

A field trip to treeline on Mt Field today revealed a less touchy snowpack than expected. No new avalanches seen and surprisingly no whumphing or reactivity on steep rolls TL and BTL. However, the Dec. 13th surface hoar layer was found in a test pit at 1950 m and produced an ECTP 26 result down 65 cm on well preserved 3-5 mm surface hoar.

Confidence

Intensity of incoming weather systems is uncertain

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.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.