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Avalanche Forecast

Archived

Dec 16th, 2019–Dec 17th, 2019

Alpine
Natural and human triggered avalanches likely.
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

North Columbia.

Snowfall combined with moderate to strong southwest wind Monday night through Tuesday will increase avalanche danger to HIGH.

Confidence

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

Weather Forecast

MONDAY NIGHT: Snow, accumulation 10-15 cm, moderate to strong southwest wind, alpine high temperature -9 C.

TUESDAY: Flurries, accumulation 10-15 cm, moderate to strong southwest wind, alpine high temperature -4 C.

WEDNESDAY: Flurries, accumulation 5-10 cm, moderate south wind, alpine high temperature -6 C.

THURSDAY: Scattered flurries, moderate southwest winds, alpine high temperature -7 C.

Avalanche Summary

On Saturday there were 3 reports of skier triggered persistent and storm slab avalanches running on surface hoar buried 25-50 cm deep. These ranged from size 1 to 2 and were on north, west and south aspects between 1400 and 2000m. Two of these were remotely triggered (from a distance). There was also a report of a snowmobile triggered size 2 persistent slab avalanche on an east aspect at 2300m

Expect to see an increase in natural avalanche activity as storm snow accumulates through Monday night and Tuesday.

Snowpack Summary

25-40 cm of recent snow has accumulated above a widespread layer of large, feathery surface hoar crystals. New snow is expected to continue to accumulate above this layer over the next few days, making it more sensitive to human-triggering.

A weak layer formed in late November is now buried around 1 m plus 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. Below this, a 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.

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.