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Avalanche Forecast

Archived

Nov 24th, 2013–Nov 25th, 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

Purcells.

You need to be the detective. Dig down, test weak layers and watch rising alpine temperatures. Feel free to send your observations to [email protected].

Confidence

Poor - Due to the number of field observations

Weather Forecast

An upper ridge of high pressure will remain over the Interior regions. At higher elevations (1600-2800m) an above freezing layer will persist through Tuesday and be pushed out by Wednesday. Monday: Mix of sun and cloud. Alpine temperatures near 0 degrees. Freezing levels rising to 2600 m. Light-moderate ridgetop winds from the West. Tuesday: Mix of sun and cloud. Alpine temperatures -1. Freezing levels 2000 m. Light westerly ridgetop winds.Wednesday: Mainly sunny. Alpine temperatures -5. Freezing levels dropping to 1500 m. Light westerly winds.

Avalanche Summary

No recent avalanche activity has been reported. The weight of a person easily triggered persistent slab problems last week. The likelihood of triggering may be decreasing, however the consequences would be huge.

Snowpack Summary

The average snowpack depths at treeline sit 70-100 cm and near a metre or more in the alpine. A surface hoar layer has been found in the Columbias 60-120 cm down and seems to be spotty, and drainage specific. I'm not sure if it exists in the Purcells. Have you seen any? Deeper in the snowpack near the base is a melt-freeze / rain crust that formed in October. This is generally found 70-110 cm down, with facetted (sugary) crystals above and below that are poorly bonded. The crust/ facet combo may be more predominant on Northerly aspects and allow for wider propagations, especially in places that have smooth ground cover (glacier ice, grassy slopes, rock slabs etc.).Snowpack conditions may change and deteriorate if temperatures rise in the alpine.

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.