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Avalanche Forecast

Archived

Dec 19th, 2018–Dec 20th, 2018

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

Regions

Lizard-Flathead.

Natural avalanche activity has tapered off to some degree, but human triggered avalanches remain likely. Conservative terrain selection is recommended.

Confidence

Moderate.

Weather Forecast

WEDNESDAY NIGHT: Mainly cloudy with isolated flurries, southwest winds, 20-40 km/h, alpine low temperature near -4°c, freezing level 1000m. THURSDAY: Cloudy with flurries beginning mid to late afternoon, 5-10 cm, southwest winds, 20-40 km/h, gusting to 60 km/h, alpine high temperature near -1°c, freezing level 1400m. FRIDAY: A mix of sun and cloud, west winds, 20-40 km/h, gusting to 80 km/h, alpine high temperature near -3°c, low temperature near -12°c, freezing level 1100m. SATURDAY: Cloudy with sunny periods and isolated flurries, southwest winds, 10-30 km/h, alpine high temperature near -8°c, low temperature near -13°c.

Avalanche Summary

Numerous natural and explosives triggered avalanches to size 2.5 were reported in the region on Wednesday. Many of these were up to 100 cm deep. A notable avalanche on Wednesday was a size 3.5 explosives triggered avalanche in which the explosives were placed on a cornice. When the cornice failed, it triggered a 200 cm deep slab that failed on the crust at the base of the snowpack. This avalanche occurred on a northeast aspect at approximately 2000m .On Tuesday, natural storm slab avalanches in alpine terrain and numerous human triggered size 1 avalanches on small steep slopes were reported in the region. On Saturday, a group of skiers remotely triggered a size 2 avalanche on a northeast facing slope at treeline in the Corbin area. The skiers were in dense trees and the avalanche released roughly 60m above them. One skier was fully buried and the group successfully extricated them without significant injuries. For full MIN incident report follow this link.

Snowpack Summary

40-50 cm of recent snow has formed fresh storm slabs. The precipitation fell as rain below 1500m, leaving moist snow on the surface. Roughly 40-90 cm of snow now sits above a weak layer composed of large surface hoar (feathery crystals), facets (sugary snow), and/or sun crusts. There have been numerous signs over the past few days that this layer remains weak, such as remote triggering from low angle terrain and wide propagations in avalanches. Several other weak layers have been observed in the lower snowpack such as early season crusts with weak facets.

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.

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.