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Avalanche Forecast

Archived

Nov 22nd, 2019–Nov 23rd, 2019

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

Regions

Little Yoho.

Watch locally for wind slabs which can step down to deeper weak layers. Depending on which forecast you look at, 20-30cm is possible by early next week along and West of the divide.

Weather Forecast

3-5 cm of snow starting in the afternoon in Little Yoho.  The wind will be moderate to strong from the West and temperatures will be -7C in the alpine and close to 0C in the valley bottom. Snow will continue Sunday and Monday with 20-30cm possible by Monday.

Snowpack Summary

15-30 cm of faceted snow overtop of a melt freeze crust from early November (crust only exists below 2300 m). Below this crust unconsolidated facets exist to ground. Treeline snow depths range from 50-80 cm, with up to 110 cm in wind loaded alpine areas. Some areas of wind slab exist at ridgetops and cross loaded features.

Avalanche Summary

No observations in Little Yoho today, but East of the divide some loose dry avalanches in the range of size 1.5-2 were observed. These were in steep, cross loaded gullies on Observation Peak, and a couple of smaller wind slabs from steep ridgetops in the same area.

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.