Avalanche Forecast

Archived

Mar 6th, 2021–Mar 7th, 2021

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

Banff Yoho Kootenay.

http://www.pc.gc.ca/apps/links/goto_e.asp?destination=

Cooler temperatures and less solar inputs on Sunday should further reduce the likelihood of triggering persistent slabs. However it is a big forecast region and there is still uncertainty as to how reactive these will be in different areas.

Weather Forecast

Clouds and light flurries are forecast for Sunday with a few cm's of accumulation starting late in the afternoon and evening. Alpine winds will be in the high end of Moderate from the SW which will help keep things cool but could move snow in the alpine. Treeline temperatures will be around -5 with valley bottom temperatures just above freezing.

Snowpack Summary

10-15 cm of new snow sits over a crust on solar aspects. Previous strong SW winds scoured alpine ridges and created wind slab in some alpine lee areas. Two persistent facet layers (Feb 19 & Jan 27) are down 30-80cm and still producing sudden shears in some locations. In thin areas the basal depth hoar/crust from Nov is still quite prominent.

Avalanche Summary

Small loose wet sluffs were observed on steep south aspects Saturday when the sun came out. No new slab avalanches were observed however lots of natural cornice, explosive, and some skier triggered avalanches, up to size 3, have been observed in the past four days during the big warm up. Most seem to be failing on one of the persistent layers.

Confidence

Timing or intensity of solar radiation is uncertain

Problems

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.

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.

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.