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Avalanche Forecast

Archived

Dec 23rd, 2020–Dec 24th, 2020

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

Regions

Little Yoho.

http://www.pc.gc.ca/apps/links/goto_e.asp?destination=http://avalanche.ca/spaw/2020-12-23-spaw

Mount Dennis closed for avalanche control Thursday. No activities permitted. We are coming out of a recent avalanche cycle and the snowpack is still adjusting to the load. Good ski quality in sheltered locations.

Weather Forecast

Alpine winds from the West will stay elevated Thursday, and alpine temperatures will stay slightly warmer (-4 to -5C) than valley bottoms (-6 to -8C), No new snow is in the forecast until the weekend. Winds look like they will decrease Friday and Saturday.

Snowpack Summary

Winds from a variety of directions have blown the ~60cm of snow from the past week into wind slabs at higher elevations. The Dec 13 and Dec 7 sun crust/surface hoar/facet layers are down ~ 50cm and ~80 cm respectively. Height of snow at tree line is 80-150cm.

Avalanche Summary

Avalanche control Tuesday and Wednesday produced mixed results from no result to size 3. Most were storm slabs, sometimes stepping down to persistent layers. No new avalanches reported or observed in Little Yoho Wednesday.

Confidence

Due to the number and quality of field observations

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.