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Avalanche Forecast

Archived

Dec 6th, 2019–Dec 7th, 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 unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

North Columbia.

Storm snow will continue to accumulate Friday night and through Saturday as a frontal system stalls over the region. This will raise the avalanche danger to HIGH.

Confidence

No Rating - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Friday Night: Snow, 10-20 cm, alpine temperature -3 C, moderate southwest wind.

Saturday: Snow, 10-15 cm, alpine temperature -4, moderate southwest wind.

Sunday: Sunny with cloudy periods, alpine temperature -10, moderate north wind.

Monday: Sunny with cloudy periods, alpine temperature -8, moderate northwest wind.

Avalanche Summary

Recent reports indicate skier triggered and natural storm slab avalanches to size 2, and cracking on small, supported slopes. There were also a few reports persistent slab avalanches failing on a layer of surface hoar (down 60-80 cm) at treeline elevations. Expect to see an increase in storm and persistent slab avalanches as the new snow continues to accumulate through Friday night and Saturday.

Snowpack Summary

25-45 cm of new snow falling over the past 36 hours has added to the 30-50 cm of storm snow from early in the week. All this new snow has covered a thick layer of faceted crystals, previously wind-affected surfaces, and/or surface hoar in sheltered areas around treeline and below.

A layer of surface hoar (feathery crystals) may be found in sheltered areas around treeline down 50-80 cm. In some areas this may be sitting on a crust.

A variety of crusts from late October are buried deeper in the snowpack. Total snow depths range from 120-150 cm around tree line.

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.