Avalanche Forecast

Archived

Mar 4th, 2021–Mar 5th, 2021

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 unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Banff Yoho Kootenay.

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Beautiful day today! Expect another crust on solar aspects. Start and finish early, expect the hazard to increase as the day warms or with prolonged solar input.

Weather Forecast

A ridge of high pressure continues to bring mainly sunny skies, rising temperatures and 30-80km/hr winds from the South West. The freezing level is expected to rise again to ~2100m on Friday with valley bottom temperatures reaching +10. Expect increasing cloud Friday afternoon with light flurries overnight and into Saturday.

Snowpack Summary

Top 5 cm moist snow on steep solar aspects and top 5-10 cm at treeline and below (except North aspects). Previous strong SW winds scoured alpine ridges and created windslab in many exposed areas. These windslabs and two persistent layers of facets and sun crust down 30-80 cm are the sliding layers for avalanches to size 3 throughout the region.

Avalanche Summary

Wed/Thurs avalanche control produced impressive results up to size 3 involving the wind slab and/or persistent slabs, some running to the end of the runnout entraining weak snow in the track. A few natural slab avalanches to size 2 on E aspects and wet loose to size 1.5 on solar aspects.

Two close calls in the Simpson area of Kootenay last weekend.

Confidence

Timing of incoming weather systems is uncertain on Friday

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.