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Avalanche Forecast

Archived

Jan 4th, 2015–Jan 5th, 2015

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 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.

Regions

Little Yoho.

Up to 60cm of snow will overlie the Dec 18 surface hoar layer in the next 2 days. We expect this layer to become prime for human triggering.

Weather Forecast

Up to 20cm of new snow is expected in the lIttle Yoho region over the next 24-48 hours. Along with a NW flow with warming temps, the danger rating will remain in the considerable range.

Snowpack Summary

The main issue currently is the Dec.18 layer which is down 35-50 cm and sits on a crust/surface hoar combination at elevations below 2100 meters and on a facet/surface hoar combination at higher elevations. In places below 2100m there is a melt/freeze crust up to 10cm thick with surface hoar above. Wind slabs have been encountered in alpine areas.

Avalanche Summary

No new avalanches have been observed or reported.. Over the last few days, many features starting to slab up with wind effect have been producing "whumpfs" over the dec 18th layer at treeline and above

Confidence

Intensity of incoming weather systems is uncertain on Monday

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.