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Avalanche Forecast

Archived

Nov 26th, 2017–Nov 27th, 2017

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

Regions

South Columbia.

Consider avalanche danger to be HIGH in areas that receive rain on top of 30 cm or more of dry snow. Avoid exposure to avalanche terrain during periods of rapid loading by rain, snow, or wind.

Confidence

Low - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

We should see a return to more seasonal temperatures this week with small accumulations of snow. MONDAY: Cloudy with isolated flurries. Light to moderate westerly ridgetop winds. Freezing level around 1000 mTUESDAY: 5-10 cm of snow. Light to moderate westerly ridgetop winds. Freezing level around 1500 mWEDNESDAY: Isolated flurries. Moderate westerly ridgetop winds. Freezing level rising around 1200 m

Avalanche Summary

On Saturday we received reports of a skier-triggered Size 1 storm slab on a NW aspect at 2150m elevation in Rogers Pass. See here for the MIN report. A natural avalanche cycle is expected on Sunday into early Monday in areas where rain falls on dry snow. We currently have very limited observations in this region. Please submit your observations to the Mountain Information Network (MIN).

Snowpack Summary

15 to 30 cm of recent snow and moderate to strong southwesterly winds have likely formed wind slabs on lee features at treeline and above. The new snow sits on a thick crust formed by the rain that fell to mountain tops on Wednesday and Thursday. The heavy rain has rapidly shrunk the snowpack and has transitioned much of the snowpack from dry to moist snow. The depth of the snowpack varies greatly with elevation. Recent reports suggest the average depth is 200+cm in the alpine, 100-150cm at treeline, and decreasing rapidly below treeline where the primary hazards are rocks, stumps, and open creeks. A major feature in the snowpack is a crust which was formed around Halloween and can be found approximately 70-100cm down at treeline elevations. We currently have very limited snowpack observations within this region and it is critical to supplement this information with your own observations.

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.