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Avalanche Forecast

Archived

Jan 26th, 2021–Jan 27th, 2021

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

Regions

South Columbia.

A dusting of flurries and increasing winds may build fresh wind slabs by the end of the day.

Confidence

Moderate - Confidence is due to a stable weather pattern with little change expected. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Tuesday night: Mostly cloudy / southeast winds, 15-25 km/h / alpine low temperature -5

Wednesday: Cloudy with isolated flurries, 5-10 cm / southeast winds, 15-25 km/h / alpine high temperature -12

Thursday: Cloudy with scattered flurries, 5-10 cm / southeast winds, 10-15 km/h / alpine high temperature -9

Friday: Cloudy with sunny breaks / south winds, 10 km/h / alpine high temperature -8

Avalanche Summary

On Sunday in Glacier National Park, a skier triggered a size 2 avalanche upon entrance into a cross-loaded terrain feature. 

On Saturday, a skier triggered a size 2 wind slab avalanche of a layer of surface hoar; the crown averaged 25 cm. The avalanche was triggered just below an open and corniced ridge feature at tree line, and occurred in the southern end of the forecast region in the Selkirks. As you step out into steeper terrain, a slope-specific assessment is recommended

Other recent avalanche activity includes small size 1-1.5 wind slabs, a few large cornice failures, and loose dry sluffing in steep and southerly terrain. 

We're continuing to track a layer of surface hoar from early January, the most recent activity reported on this layer was January 18, when several operators in the region reported small (size 1-1.5) human-triggered avalanches releasing on a weak layer of surface hoar on north, east and southeast aspects at treeline and below treeline elevations. These avalanches were breaking 25-45 cm deep.

Snowpack Summary

 A dusting of low density snow overlies a widespread layer of surface hoar up to 10 mm in sheltered areas around treeline. The snowpack boasts a variety of surfaces including scoured and pressed surfaces in exposed terrain, large cornices, isolated wind slabs, and variable wind affected and facetted snow in more sheltered terrain. Cold temperatures are encouraging surface faceting and breaking down wind slabs. A thin sun crust may be found on steep solar aspects. Below 1700-1800 m, 20-30 cm of snow is settling above a decomposing melt freeze crust.

Observers continue to find a preserved layer of surface hoar down 25-50 cm in sheltered, open slopes at and below treeline. Most recent reactivity has been reported in the Selkirks towards the south of the forecast region (see avalanche summary). On the other hand, snowpack tests on this layer are trending to hard and resistant shears, as such it continues to warrant slope-specific assessment.

Deeper in the snowpack, a couple of older persistent weak layers may still be identifiable from late and early December, consisting of surface hoar and a crust with faceted snow and buried anywhere from 100-200 cm deep. Prolonged periods of inactivity and unreactive snowpack test results suggest that these layers have trended towards dormancy.

Terrain and Travel

  • Carefully evaluate steep lines for wind slabs.
  • Large cornice falls are dangerous on their own.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.