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Avalanche Forecast

Archived

Dec 17th, 2018–Dec 18th, 2018

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

Regions

South Rockies.

Dial back your terrain choices if slopes are getting loaded by new snow and wind on Tuesday.

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Tuesday

Weather Forecast

MONDAY NIGHT: 5-10cm of snow as a front approaches, strong wind from the southwest, freezing level around 1300m. TUESDAY: 5-10cm of snow, extreme wind from the southwest, freezing level up to 1600m, alpine high temperature around -3 C. WEDNESDAY: Mix of sun and cloud, strong wind from the west, freezing level up to 1500m, alpine high temperature around -5c. THURSDAY: Mix of sun and cloud, moderate wind from the west, freezing level up to 1500m, alpine high temperature around -5c.

Avalanche Summary

On Monday, a skier triggered a large slab avalanche (size 2) on a east aspect around 1800 m. The avalanche failed on a persistent weak layer 40 cm below the surface.On Friday and Saturday, explosive control produced numerous large (size 2-3) wind slab and deep persistent slab avalanches on north and east aspects above 2000 m.Natural activity was also reported on Friday, primarily size 1-2 wind slab avalanches on east-facing lee terrain in the alpine. Some appear to have stepped down to the deep persistent weak layers near the bottom of the snowpack. See some photos of these from north of Crowsnest Pass.

Snowpack Summary

Tuesday's storm will build fresh wind slabs at higher elevations. Strong wind has affected all open terrain over the past few days, scouring windward slopes and forming wind deposits on lee slopes. Currently only 30-120 cm of snow can be found in alpine areas and much less at lower elevations.The lower snowpack has a weak structure composed of facets and crusts. Heavy explosive triggers have produced large avalanches on these layers, and human triggering is suspect on steep terrain features and slopes with variable snowpack depth.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.