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Avalanche Forecast

Archived

Dec 20th, 2019–Dec 21st, 2019

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

Regions

Glacier.

High Avalanche Danger today through Saturday! A great day to avoid avalanche terrain.

Weather Forecast

An atmospheric river of moisture from the Pacific has begun to dump on the Selkirks. The forecast calls for 30cm in the next 24 hours with an additional 20cm through the day Saturday. Moderate to strong SW winds will accompany this storm front accompanied by freezing levels rising to 1500m. The storm should abate late Saturday.

Snowpack Summary

Field tests and observations found a reactive storm slab down 20cm. 80cm+ of snow now buries the Dec 11 surface hoar layer. Previous new snow, and mod winds built storm slabs at all elevations. The Nov 23rd surface hoar/crust/facet combo is down +/-130cm has become increasingly stubborn in testing. These interfaces are expected to wake up today.

Avalanche Summary

A fresh avalanche cycle began last night at 10pm and is ongoing. We expect a widespread avalanche cycle to continue at all elevations through to Saturday afternoon when the winter storm is forecast to abate.

Confidence

Forecast snowfall amounts are uncertain

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.

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.

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.