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Avalanche Forecast

Archived

Apr 13th, 2021–Apr 14th, 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 possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.

Regions

Banff Yoho Kootenay.

Wednesday will start with LOW hazard, but intense solar radiation and rising freezing levels will raise the hazard. Start and finish early, and avoid steep solar aspects and terrain threatened by cornices as they warm up.

Weather Forecast

Light easterly winds & sunny skies continue for Wednesday. Freezing levels will rise to 2500 m with intense solar inputs expected at all elevations during the day. Good overnight freezes with slowly increasing freezing levels and lots of solar inputs are expected for the next several days as we progress to the spring diurnal hazard rating.

Snowpack Summary

15 to 30 cm of storm snow at treeline with more at higher elevations. Buried crusts up to 1800m on all aspects and to ridge crest on solar aspects. Small wind slabs in alpine lee areas. Several persistent layers exist in the mid to lower snowpack that might be a concern in thin areas with significant warming or with larger triggers like cornices.

Avalanche Summary

One size 3 deep persistent slab triggered by cornice failure at 10 am today on Mt. Stanley. Another size 2.5 cornice triggered slab on the Mt. Whymper from Monday afternoon.  Several loose dry avalanches observed with in steep terrain as the sun warmed the surface. A few days ago, storm snow failed on a buried crust so this is worth monitoring.

Confidence

Problems

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.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.