Avalanche Forecast

Archived

Jan 18th, 2022–Jan 19th, 2022

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Jasper.

Cross and reverse wind loading from north winds Monday evening resulted in a large avalanche cycle in the alpine around the Churchill Range. Normally shallow alpine slopes could be primed to avalanche with a hard wind slab sitting on faceted snow.

Weather Forecast

Wednesday

Cloudy with sunny periods.

Precipitation: Nil.

Alpine temperature: High -9 C.

Light ridge wind.

Freezing level at valley bottom.

Thursday

Mainly cloudy with isolated flurries.

Precipitation: Trace.

Alpine temperature: Low -13 C, High -8 C.

Ridge wind southwest: 10 km/h.

Freezing level at valley bottom.

Snowpack Summary

North winds have built cross and reverse wind slabs into tree line. The mid snowpack is faceted with two notable persistent weak layers. A buried facet interface is down 20-30cm. A faceting crust is down 40-60cm below 1950m. Basal facets and depth hoar can be found at the base of snowpack.

Avalanche Summary

Several large avalanches were observed around the Churchill Range up to sz 2.5 and running to ground. These are likely the results of normally shallow thin wind blown slopes being loaded from north winds on Monday evening.

Confidence

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

Problems

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.

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.