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Avalanche Forecast

Archived

Mar 4th, 2024–Mar 5th, 2024

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 possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Banff Yoho Kootenay, Little Yoho, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

The avalanche cycle and the period of highest danger is past its peak, but now comes the hardest part for backcountry recreation: human triggering remains very likely, but not as obvious. The Feb 3 interface is pervasive, and producing large avalanches and close calls throughout the Rockies. Avoid avalanche terrain.

Confidence

High

Avalanche Summary

Several natural avalanches up to size 3 were observed in the alpine on Monday that occurred in the previous 12 hrs, likely on the Feb 3 interface.

Explosive control produced avalanches from size 1-3 in various places on Monday at all elevations.

These avalanches were failing on storm interfaces as well as the Feb 3 interface and occasionally the deep persistent layers.

Several close calls with human triggering of avalanches from size 2-3 have occurred in the past three days.

Snowpack Summary

50-90 cm of new snow fell from Feb 23 to March 2 and is now being blown into wind slabs at upper elevations by strong westerly winds overnight Monday. These easily triggered slabs overlie the weak Feb 3 facet/crust layer that is down 50-90 cm and exists up to 2500 m and higher on solar aspects. The lower snowpack consists of several facet layers and depth hoar and the base of the snowpack is weak in shallow areas.

Weather Summary

Although a clearing trend is underway this week, strong (50 km/hr) upper-level winds are forecast from the west overnight Monday, through Tuesday. Other than the wind (which matters a lot), the weather improves as a ridge of high pressure establishes itself. For Tuesday expect trace amounts of snow, broken skies and temperatures of -10 to -20; same for Wednesday and full clearing by Thursday.

Terrain and Travel Advice

  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
  • Remote triggering is a big concern, be aware of the potential for wide propagations and large, destructive avalanches at all elevations.

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.