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Avalanche Forecast

Archived

Nov 23rd, 2019–Nov 24th, 2019

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

Regions

Little Yoho.

Avalanche activity is expected to increase Sunday with 10-20 cm of snow and strong winds forecast. Stick to more moderate angled terrain and minimize exposure to steep alpine/ treeline terrain or narrow gullies where sluffs can pick up mass.

Weather Forecast

Strong west winds and between 10-20 cm of new snow are forecast for Saturday night and Sunday with areas near the divide receiving the bulk of the snow. Temperatures will remain mild on Sunday and slowly start to cool on Monday as clear cold weather moves in for the week.

Snowpack Summary

Wind slabs will continue to build overnight with new snow and strong SW winds. 15-30 cm of faceted snow sits over a melt freeze crust from early November. This crust is present to ~2400 m. Below this crust the snowpack is generally weak facets to ground. Treeline snow depths range from 40-80 cm, with up to 110 cm in wind loaded alpine areas.

Avalanche Summary

No new avalanches reported on Saturday but observations were limited. Friday some loose dry avalanches in steep, cross loaded gullies on Observation Peak, and a couple of smaller wind slabs from steep ridge tops in the same area were reported between size 1-2. We expect avalanche activity to increase on Sunday with the new snow and strong winds.

Confidence

Forecast snowfall amounts are uncertain on Sunday

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.