Avalanche Forecast

Archived

Apr 21st, 2023–Apr 22nd, 2023

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Below Threshold.

Regions

Jasper, Brazeau, Churchill, Cirrus-Wilson, Fryatt, Icefields, Maligne, Marmot, Miette Lake, Pyramid.

Isolated large to very large avalanches are still possible in moderate avalanche danger. Recent large cornice triggered deep persistent slabs are a good reminder to keep your head on a swivel when stepping out into a more complex terrain.

Confidence

Moderate

Avalanche Summary

On Friday , 2 natural large deep persistent slab avalanches were observed by the Icefields road patrol, both on east aspect in the alpine triggered by a cornice failure.

Maligne road patrol saw no new natural avalanche activity on Friday.

Don't forget to post avalanche observations to the MIN.

Snowpack Summary

Around 15cm of new snow this week sits on crusts on solar aspects, a melt freeze crust below tree line and old wind slab in exposed alpine

Below tree line is in a daily melt-freeze cycle. At tree line the mid-pack consists of multiple layers of sun crusts or facets. Depth hoar and basal facets at the base.

Weather Summary

Saturday: Cloudy with sunny periods. Precipitation: Nil. Alpine temperature: High -2 °C. Ridge wind light to 20 km/h. Freezing level: 2000 m.

Sunday: Cloudy with sunny periods and isolated flurries. Precipitation: Trace. Alpine temperature: Low -4 °C, High 1 °C. Mostly light ridge wind occasionally gusting to 25 km/h. Freezing level: 2400 m.

Terrain and Travel Advice

Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
Cornices become weak with daytime heating.

Problems

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.

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.