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Avalanche Forecast

Archived

Dec 10th, 2019–Dec 11th, 2019

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

Regions

North Columbia.

Don't underestimate the potential for human triggered avalanches. Keep your guard up especially as you transition into wind exposed terrain, and evaluate conditions before committing to larger features.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Tuesday Night: Cloudy with scattered flurries accumulating up to 5 cm in some areas, alpine low -10, light to moderate southwest wind.

Wednesday: Cloudy with flurries accumulating to 5 cm in the southwest of the region, alpine high -5, light to moderate southwest wind increasing overnight.

Thursday: Periods of snow accumulating 5-15 cm, alpine high -5, strong southwest wind easing to moderate.

Friday: Flurries accumulating to 5 cm in the south of the region, alpine high -5, light west wind.

Avalanche Summary

Although natural avalanche activity has largely subsided, natural persistent slabs are still being reported, up to size 2.5 on south aspects. On Monday, a variety of artificially triggered avalanches, up to size 2, were reported on northeast aspects. One explosive controlled avalanche was triggered in a wind slab and stepped down to the persistent weak layer further down the track.

Snowpack Summary

Last week's storm snow has seen some redistribution by the wind. Isolated soft wind slabs can be found in the lee of features such as ridge tops. Below the 50-90 cm of snow from last week, a thick layer of faceted crystals, previously wind-affected surfaces, and/or surface hoar in sheltered areas (around treeline and below) is now 40-80 cm below the surface. The surface hoar layer within the storm snow can still be found in some locations but has not shown recent reactivity.

A weak layer formed in late November is now buried 70-120 cm below the surface. This is the layer of concern relating to the persistent slab avalanche problem. The weak layer may present as surface hoar, a crust, facets or a combination, depending on elevation and aspect. It can most likely be found in areas sheltered from the wind, but open to a view of the sky, such as near treeline. Below this, variety of crusts from late October are buried deeper in the snowpack.

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.