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Avalanche Forecast

Archived

Mar 4th, 2020–Mar 5th, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Banff Yoho Kootenay.

Explosive avalanche control is planned for Thursday March 5 on Mt. Bourgeau (above the Sunshine Village Road), Mt. Whymper and Mt. Simpson (Highway 93 South). Respect the closure signs and do not enter these areas.

Weather Forecast

Mainly cloudy on Thursday with another 5-10cm of snow, temp range of -16 to -4 and consistently strong SW winds. Thursday night into Friday will see another 10cm and gradually decreasing winds. Another 10cm forecasted for Saturday with cooling temps and light winds.

Snowpack Summary

30-40 cm of storm snow in the past few days brings the weekly total to ~60cm. Strong to extreme Westerly winds continue to form storm/wind slab at all elevations. Watch for buried sun crust on steep solar aspects. In thin snow pack areas a dense mid-pack sits over a weak, faceted base. Thick snowpack areas have a denser base with few weaknesses.

Avalanche Summary

Several natural storm slab avalanches up to sz 2.5 observed along highway 93S today where intense wind loading was occurring.

With continued strong to extreme winds and incoming snow in the forecast over the next few days, expect natural avalanche activity to increase.

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Thursday

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.