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Avalanche Forecast

Archived

Jan 18th, 2019–Jan 19th, 2019

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

Regions

Purcells.

The Purcell snowpack is still scary and requires conservative terrain choices. Read the Forecaster's Blog about the region for more details here...

Confidence

High -

Weather Forecast

FRIDAY NIGHT: 5-10 cm of snow, moderate southwest wind, alpine temperatures drop to -10 C.SATURDAY: Flurries easing throughout the day with another 5 cm of snow, strong southwest wind, freezing level climbing to 1200 m, alpine high temperatures around -5 C.SUNDAY: Mostly cloudy then clearing in the afternoon, moderate west wind, freezing level climbing to 800 m, alpine high temperatures around -7 C.MONDAY: Mix of sun and cloud, light northwest wind, alpine high temperatures around -8 C.

Avalanche Summary

The likelihood of triggering large avalanches is still elevated due to the weak nature of the snowpack. Watch out in thin snowpack areas, where the likelihood of triggering deeper layers is the highest.On Thursday, explosives triggered numerous large cornices on north alpine ridges. On Wednesday, a large (size 3) naturally triggered avalanche was observed on a southeast aspect in the alpine near Golden. On Monday, several large (size 2) avalanches were observed throughout the region, some releasing on weak faceted grains near the base of the snowpack. On Sunday, a large (size 3) avalanche ran full-path on a southwest aspect in the alpine near Golden.Last weekend, a group of snowmobilers triggered a fatal avalanche near Invermere, also on the basal weak faceted grains. The avalanche was on a southerly aspect and ran approximately 900 to 1100 m. Two snowmobilers were caught. See here for more information.

Snowpack Summary

The snowpack is weak and touchy in large portions of the Purcells, with very large avalanches being reported on a regular basis. This type of weak snowpack could stick around for months. Read more here. 5-20 cm of new snow is burying large surface hoar crystals and/or sun crusts, which could eventually develop into a touchy problem as snow accumulates. The most suspect terrain features will be steep slopes and rolls below 2000 m (where the largest surface hoar exists) and steep south-facing slopes in the alpine (where sun crusts exist).The weak nature of the snowpack lies at depth. There is a weak layer around 80 to 120 cm deep, composed of sugary faceted grains, feathery surface hoar, and a sun crust. The base of the snowpack is also composed of weak faceted grains in many parts of the region. Humans have and will continue to be able to trigger these layers in areas where the snowpack is shallow.

Problems

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.

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.