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Avalanche Forecast

Archived

Dec 11th, 2019–Dec 12th, 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.

The Monashees along the southern border of the region will see enhanced snowfall amounts compared to the rest of the region. Reactive storm slabs building through the day will elevate the danger rating to Considerable at alpine and treeline in this area.

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

Wednesday Night: Cloudy with flurries starting, accumulating 5-10 cm by morning, concentrated in the southwest of the region. Alpine low -7, light to moderate southwest wind.

Thursday: Periods of snow accumulating 5-15 cm concentrated in the southwest of the region. Alpine high -5, moderate southwest wind gusting strong.

Friday: Flurries accumulating to 5 cm, alpine high -5, light west wind.

Saturday: Mainly cloudy, isolated flurries with trace accumulation, alpine high -5, light northwest wind.

Avalanche Summary

Numerous natural, explosive and skier triggered avalanches size 2-2.5 on a variety of aspects have been reported recently throughout the region and in neighboring Glacier National Park. Some of these avalanches were triggered in areas of shallow snowcover or wind slab and stepped down to the persistent November layer resulting in avalanches large enough to injure or bury a person.

Snowpack Summary

Large, feathery surface hoar crystals have been observed on the snow surface at all elevations throughout the region, and are now covered by a dusting of snow. As new snow falls on this layer over the day Thursday, reactive storm slabs may build in areas of higher snowfall.

Soft wind slab can be found in the lee of features such as ridge tops, ribs and gulleys. Elsewhere, the upper snowpack remains soft and unconsolidated in the cool temperatures.

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

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.