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Avalanche Forecast

Archived

Jan 29th, 2013–Jan 30th, 2013

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

Regions

Little Yoho.

Strong NW winds are forecasted to blow tonight, causing the danger to rise on Wed. In sheltered areas, and areas with insufficient new snow to blow around, the danger rating may be lower.

Weather Forecast

A northwesterly flow is bringing thin overcast skies, light precip and moderate to strong NW winds throughout the forecast period. Temperatures will gradually warm with alpine highs in the -5/-10 range and lows in the -10/-15 range.

Snowpack Summary

In alpine there is 20-25 cm of recent storm snow sitting on previous hard wind slabs and wind pressed snow. Some soft slab development in lee terrain near ridge tops. In shallow snow pack areas the mid-pack is facetting and losing strength.

Avalanche Summary

Forecasters observed a size 2 naturally triggered avalanche on a N aspect around 2300m on the Sunshine road. This avalanche was likely triggered by a cornice fall and likely occurred within the last 24 hours.

Confidence

Wind speed and direction is uncertain on Wednesday

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.