Avalanche Forecast

Archived

Apr 16th, 2023–Apr 17th, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Regions

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

Incoming snow or rain and wind Sunday evening. Approach your day with diligence regarding these overnight changes.

Confidence

Moderate

Avalanche Summary

Explosives control in a permanently closed area at Marmot Basin on Sunday reported triggering a size 2 persistent slab, stepping down to basal weaknesses.

A size 2 skier accidental triggered deep persistent slab avalanche was reported on the regular approach to the north glacier on Mt. Athabasca on Thursday.

Natural activity has tapered off but still requires vigilance and careful assessments.

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

Snowpack Summary

New snow is forecasted for overnight Sunday, up to 5-10cm, expect rain below freezing level. Upper snowpack consists of 20cm of snow from the previous storm sitting on multiple crusts up to 2400m. Snow pit tests are showing results in the weak facet crystals below these crusts on south aspects. The snowpack below 1800m is in a daily melt-freeze cycle. The mid-pack above this elevation consists of multiple layers of sun crusts or facets. Depth hoar and basal facets make up the base of the snowpack.

Weather Summary

Sunday night will see rising freezing levels to 2300m and flurries producing up to 7 cm at higher elevations and rain below. Ridge wind from the southwest (20 km/h gusting to 55 km/h).

For Monday expect a mix of sun and cloud and a alpine high of -8 °C. Ridge wind from the southwest (20 km/h gusting to 50 km/h). Freezing level will be at valley bottom.

Tuesday will be another day of cloudy with sunny period conditions. Alpine temperatures are forecasted to be a low of -11 °C and high of -5 °C. Ridge wind will be from the southwest (10-25 km/h) and freezing level at 1600 metres.

Terrain and Travel Advice

Keep in mind that human triggering potential persists as natural avalanching tapers off.
Stay off recently wind loaded slopes until they have had a chance to stabilize.
Remember that in the spring strong solar radiation and warm temperatures can weaken the snow in a matter of minutes.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.

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.