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Avalanche Forecast

Archived

Jan 25th, 2020–Jan 26th, 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, 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.

Regions

South Coast Inland.

Ongoing flurries and gusty winds continue to develop and build storm slabs.

Confidence

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

Weather Forecast

SATURDAY NIGHT: Scattered flurries, 5 cm. Alpine low temperature -6 C. Southeast wind 10-20 km/hr. Freezing level 1000 m.

SUNDAY: Snow, 5-20 cm with the higher snowfall amounts favoring the Coquihalla. Alpine high temperature -3 C. South wind 20 gusting to 60 km/hr. Freezing level 1400 m.

MONDAY: Scattered flurries, 5-10 cm. Alpine high temperature -4 C. Southwest wind 20 gusting to 50 km/hr. Freezing level 1100 m.

TUESDAY: Flurries and snow, 5-20 cm. Alpine high temperature -4 C. Southwest wind 10-20 km/hr. Freezing level 1200 m.

Avalanche Summary

On Friday, small loose wet avalanches failed on south aspects at lower treeline and below treeline elevations.

Three very large (size 2-3) deep persistent avalanches failed naturally sometime between Thursday and Friday in the Duffey Lake area and near Gold Bridge. These avalanches occurred on east and northwest aspects around 2150-2200 m. Additionally, skiers remotely triggered a size 3 avalanche on a north aspect at 2100 m in the Duffey area and a size 1 deep persistent avalanche triggered by skiers while traveling along a skin track on a west aspect at 2050 m near Whitecap Mountain. Weak faceted grains and crusts near the base of the snowpack have periodically produced avalanches and continue to be a concern with additional loading from new snow and wind.

On Thursday, small (size 1) storm slab avalanches failed naturally on northerly aspects. Additionally, a machine triggered a size 2 avalanche on a steep slope below a road at 1800 m. Small (size 1-1.5) wet loose avalanche activity was reported below treeline.

Snowpack Summary

10-30 cm recent snow has settled with warm temperatures over a crust from January 20. Southerly winds have redistributed snow and formed windslabs in open areas and along ridgelines. Below 1600 m, rising freezing levels and rain produced moist surface snow and rapid snowpack settlement.

There have been two layers of concern in the northern half of the region (e.g. Duffey, Hurley). One is a weak layer of surface hoar buried about 100 cm deep that professionals are tracking at treeline in sheltered areas. The other is weak faceted grains and crusts near the bottom of the snowpack, that is most likely to be triggered in shallow rocky start zones. There are currently no concerns about deep weak layers in the south of the region (e.g. Coquihalla).

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

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.