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Avalanche Forecast

Archived

Jan 10th, 2019–Jan 11th, 2019

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

Regions

South Columbia.

Avalanche danger is expected to rise over the weekend with anticipated warm weather. Pay particular attention to sun affected slopes.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

THURSDAY NIGHT: Dry, cooling overnight.FRIDAY: Dry with a mix of sun and cloud. Freezing levels rising to around 1500 m. Alpine temperatures around -2C. Light southerly winds.SATURDAY: Dry and sunny. Inverted conditions with an above freezing layer between 1800m and 2500m. Light southerly winds.SUNDAY: Dry and sunny. Inverted conditions with an above freezing layer between 1800m and 2500m. Light southwesterly winds.

Avalanche Summary

A size 3-3.5 persistent slab avalanche was skier triggered on the north side of the highway in Glacier National Park on Tuesday. This was triggered from a thin spot on the ridge at 2250 m on a south east aspect. It ran to the valley bottom and is suspected to have run on a layer of surface hoar sitting on a crust that was buried in late November. See the MIN post here. Although outside of the South Columbia region it is a notable avalanche that illustrates the potential for thin spot triggering of deeper weak layers that may be reactive in isolated areas in this region. The onset of warmer weather may increase the chances of triggering a larger avalanche.

Snowpack Summary

Although the snow tap appears to have been switched off for a while, recent new snow will have formed new wind slabs in lee and cross-loaded terrain features at high elevations. This new snow has fallen on widespread wind-affected snow at alpine and treeline elevations. Below this, the snowpack is generally well-settled. There is however, a layer of feathery surface hoar that is sitting on a crust that was buried late November down 100-200 cm. This crust is suspected to be the bed surface for few notably large avalanches over the past 2-3 days on southwest through southeast aspects in the North and South Columbia regions.

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.