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

Regions

South Rockies.

Please note this bulletin is based on limited information. If you have been out and have observations, please send them to [email protected]

Confidence

Poor - Due to the number of field observations

Weather Forecast

A ridge of high pressure will dominate the pattern through the period.Saturday: Dry and sunny. A temperature inversion will bring warm alpine temperatures of up to 5C, valleys may be substantially cooler. Winds light northwesterly.Sunday and Monday: Pretty much the same as Saturday, except the strength of the inversion will likely diminish and winds may pick up slightly for Sunday.

Avalanche Summary

Avalanche activity was reported in pockets of deeper snow from Monday (18th) and Tuesday (19th) in both western and eastern areas of the region. Activity appears to have tapered off. Recent slope tests have produced results only in isolated pockets of wind slab on steep convex rolls.

Snowpack Summary

Treeline snowpack depths in sheltered areas vary between approximately 40-80 cm. In the alpine, coverage is highly variable due to recent high winds. A crust or significant density change may exist around 40 cm below the surface. This has been reported to have weak faceted crystals above and below, and produces sudden "pop" results in compression tests. Below this near the base of the snowpack, an earlier crust buried in October lies close to the ground. This layer may still be of concern on isolated smooth terrain features that have not seen avalanche activity.

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.