Avalanche Forecast

Archived

Jan 4th, 2014–Jan 5th, 2014

Alpine

Natural avalanches possible, human triggered probable.

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 possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Purcells.

While humans crave simplicity the current situation is anything but. The answer to the avalanche problem this weekend is staying conservative with terrain selection. Visit the blog for thoughts on the recent pattern of accidents in the Purcells.

Confidence

Good - Freezing levels are uncertain on Monday

Weather Forecast

A strong, stable northwesterly flow will prevail over the province while a strong upper ridge remains offshore. The mountain top winds should ease Sunday as the upper ridge moves over the coast. The ridge will then weaken somewhat on Monday but will still protect the province from Pacific systems.Sunday: Freezing Level: Valley Bottom; Precip: Nil; Wind: Light, Variable. Strong NW at ridgetop.Monday: Freezing Level: Valley Bottom with chance of an Above Freezing Layer from 1500 2500m. Precip: Nil; Wind: Light Variable, Mod NW at ridgetop.Tuesday: Freezing Level: Valley Bottom; Precip: Trace; Wind: Lht Variable.

Avalanche Summary

There have been a few different close calls with large avalanches in the north of this region in the last two weeks. Check out the incident database for more details. On Friday avalanches released naturally and with explosive control resulting in avalanches to size 3.5 with crowns up to 2 meters in depth on all aspects.

Snowpack Summary

Thursdays 20 - 40 cm of storm snow lies on top of old wind slabs and a couple of persistent weak layers that exist in the upper meter of the relatively thin snowpack. The Mid December Surface Hoar is buried around 30-90 cm. The early December facet/crust combo is buried down 50-150 cm. Both interfaces give variable results with snowpack tests, but professional operators are treating them with caution.A bigger concern, especially in the Northern part of the region is a layer of weak sugary depth hoar crystals at the base of the snowpack that lie above a crust from early October. Several large avalanches in the last two weeks have been attributed to failures at this layer. Wide propagations on relatively gentle terrain have been noted, as well as a tendency for seemingly disconnected slopes to become connected by one large avalanche.

Problems

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.