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Avalanche Forecast

Archived

Mar 12th, 2023–Mar 13th, 2023

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

Regions

Glacier.

Avalanche Danger will increase throughout the day, likely reaching HIGH by the afternoon as the storm intensifies.

The Deep Persistent Layer has been brought back as a problem for Monday's storm as 30-40cm of snow is forecasted to fall with rising freezing levels, which may be enough to overload this layer.

Confidence

Moderate

Avalanche Summary

Avalanche activity will increase as the storm progresses through the day on Monday.

A close call occurred Sunday morning in MacDonald Gully 11 as a group on their way up narrowly evaded being hit by a size 2 avalanche that originated in the cliffs high above from extreme terrain. They saw the powder cloud coming down and quickly moved into the trees and out of the way. They made a good decision and turned around.

Snowpack Summary

The new snow has fallen on a variety of surfaces including wind-hardened snow in the alpine, a crust on solar aspects and surface hoar (~5mm) in sheltered shaded areas.

Although generally strong, the snowpack still sits on a deep persistent weakness of rounding facets and a decomposed crust near the ground. This layer has not been reactive since the last major snowfall (February 27th), but as the snow continues to fall, we might see some large avalanche activity on this layer.

Weather Summary

A storm front arrives late Sunday evening, persists until Monday night and is expected to drop up to 30-40cm of snow. Winds will be 50km/hr from the SW in the morning and gradually drop to ~25km/hr by the evening. The freezing level will rise to 1900m.

Cooler temps and light winds for Tuesday and Wednesday.

Terrain and Travel Advice

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • Loose avalanches may start small but they can grow and push you into dangerous terrain.
  • Caution around slopes that are exposed to cornices overhead.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.