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Avalanche Forecast

Archived

Dec 9th, 2020–Dec 10th, 2020

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 unlikely, human triggered possible.

Regions

Glacier.

The storm is over leaving a touchy storm slab over surface hoar combo. Cautious, conservative route selection is required today.

Weather Forecast

Mainly cloudy with isolated flurries and a trace of precipitation.

Alpine temperatures reaching up to -4C with light westerly winds.

Freezing level up to 1600m today.

Cloudy with sunny periods Thursday and Friday with light winds, no precipitation and alpine highs of -9C.

Snowpack Summary

35cm+ of warm snow and mod/strong SW winds have formed a storm slab. It sits on a significant widespread surface hoar (SH) layer at tree-line and lower elevations. In the alpine, the storm slab rests on a crust on steep solar aspects. Several SH layers exist in the mid-upper pack, while the Nov 5 crust lurks as a deep persistent weakness.

Avalanche Summary

Yesterday natural avalanche activity to size 3.5 was observed in the highway corridor. Avalanche control produced avalanches to size 3.5. A MIN report yesterday of a skier remote size 1 from 15m distance in Teddy Bear Trees also shows the sensitivity of the buried surface hoar layer.

Confidence

Due to the number of field 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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.