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Avalanche Forecast

Archived

Jan 26th, 2020–Jan 27th, 2020

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

Regions

Sea To Sky.

Snowfall and wind will drive avalanche hazard, the most reactive deposits will be around ridgelines and steep rolls.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

SUNDAY NIGHT: Snow, 10-15 cm. Alpine low temperature -5 C. South wind 35-55 km/hr. Freezing level 1000 m.

MONDAY: Snow and flurries, 5-15 cm. Alpine high temperature -4 C. South wind 20-40 km/hr. Freezing level 1000 m.

TUESDAY: Flurries, 5-10 cm. Alpine high temperature -3 C. Southeast wind 20 gusting to 50 km/hr. Freezing level 1400 m.

WEDNESDAY: Snow, 20-30 cm. Alpine high temperature -2 C. South wind 35-50 km/hr. Freezing level 1100 m.

Avalanche Summary

A few large to very large (size 2-3) natural storm slab avalanches were observed in the Whistler backcountry on Saturday morning, and explosives triggered storm slabs and cornice-triggered avalanches up to size 2.

On Thursday and Friday, explosives easily triggered large (size 2) storm slab avalanches, producing 40-60 cm thick slabs with wide propagation. Large storm slab avalanches (size 2) failed naturally or were triggered by falling cornices.

Explosive control on Wednesday resulted in a very large (size 3.5) deep persistent slab on a west aspect the alpine, suggesting the deep persistent slab remained reactive and sensitive to new loads. With more loading on the way natural storm and deep persistent slab avalanches remain concerns.

Snowpack Summary

Strong to extreme winds have left a variety of wind-affected surfaces in alpine and open treeline areas. Windward slopes are scoured down to the January 20 crust and wind slabs have developed in more leeward terrain. Moist surface snow has been pressed into slabs and notable cornice growth has been observed. A surface crust has developed on all aspects below 1700 m, and direct solar (south-facing) slopes at treeline and above. Forecasted flurries and southerly winds will accumulate over these surfaces and load previously developed slabs.

Weak faceted grains and crusts near the base of the snowpack continue to be a concern in inland parts of the region such as the Spearhead Range.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Extra caution is needed around cornices under the current conditions.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.

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.