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Avalanche Forecast

Archived

Dec 18th, 2018–Dec 19th, 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.

Recent snowfall has stressed the snowpack, leaving it primed for human triggered avalanches. Conservative terrain choices are recommended.

Confidence

Moderate -

Weather Forecast

TUESDAY NIGHT: Lingering flurries could produce another 10cm of snow, strong wind out of the southwest, freezing level dropping to 1000m, alpine temperatures drop to -5c. WEDNESDAY: Flurries easing throughout the day with localized accumulations of 5cm, moderate wind from the southwest with strong gusts, freezing level up to 1200m, alpine high temperatures around -5c. THURSDAY: The next system arrives late in the day, strong wind from the southwest, freezing level climbs to 1500m, alpine high temperatures around -2c. FRIDAY: 10-20cm of snow, moderate wind from the northwest, freezing level drops to valley bottom with alpine high temperatures around -8c.

Avalanche Summary

Tuesday's storm produced natural storm slab avalanches in alpine terrain and numerous small skier triggered avalanches (size 1) on small steep slopes.On Saturday, a group of skiers remotely triggered a large (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 60 m 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

Tuesday's storm hit the region with 40 cm of new snow, forming fresh storm slabs at upper elevations. The precipitation fell as rain below 1500 m, leaving moist snow on the surface.Roughly 50-80 cm of snow now sits above a weak layer composed of large surface hoar, facets, and/or sun crusts. There have been numerous signs over the past few days that this layer remains weak (e.g. remote triggering from low angle terrain, wide propagations in avalanches), and the additional load of the new snow could be pushing this layer past the tipping point.Several other weak layers have been observed in the lower snowpack such as early season crusts with weak facets. The most concerning crust is prevalent at higher elevations and is likely most problematic on north-facing features, especially those that are large and planar in nature.

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.