Avalanche Forecast

Archived

Apr 4th, 2014–Apr 5th, 2014

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 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 possible, human triggered probable.

Regions

South Rockies.

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Confidence

Fair - Freezing levels are uncertain

Weather Forecast

Overnight and Saturday: Moderate Westerly winds overnight and freezing levels dropping down to 1500 metres. Strong Southwest winds developing in the afternoon as the freezing level rises up to 2000 metres.Sunday: Freezing levels remaining near 2000 metres. Some light precipitation overnight ending as winds shift to the Northwest.Monday: Freezing levels climb to 3000 metres as warm air moves into the region. Chance of broken skies and periods of strong solar radiation. Winds light to moderate from the Southwest.

Avalanche Summary

Some very large avalanches up to size 3.0 were reported from the Harvey pass area. These natural avalanches may have been a couple of days old, and it is suspected that they either ran on or stepped down to the February deep persistent weak layer. Avalanches releasing on this layer may become more likely during the forecast very warm weather early next week.

Snowpack Summary

Solar radiation and high freezing levels have created new melt-freeze crusts on Southerly aspects. The 20-40cm of recent new snow sits on top of a thick sun crust on solar aspects. 70-90 cm of settling storm snow from the past week rests on a graupel layer that can be found in much of the region. This makes for around 90 cm on top of the mid march crust at this point. This crust exists on all aspects below 2000m and on solar aspects in the high alpine. North of Sparwood and in the Crowsnest Pass area, the buried crust seems more specific to previously sun-exposed slopes. The deep facet/crust persistent weakness buried at the beginning of February (now down 140 to 170cm) seems unlikely to trigger in areas where the hard, supportive crust exists. No matter where you are in the region, this weakness should stay on your radar as any activity at this interface would be large and destructive. Possible triggers include a large cornice fall, a large input in a thin snowpack area or solar warming.

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.

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.