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Avalanche Forecast

Archived

Feb 6th, 2018–Feb 7th, 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 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

Lizard-Flathead.

Wind and new snow are expected to begin on Wednesday into Thursday. Choose conservative, well-supported terrain. Avoid overhead hazards, like cornices, which have triggered large avalanches running long distances.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

TONIGHT: Mainly cloudy, light flurries. Accumulation 2-6 cm. Ridge wind strong, southwest. Temperature -8. Freezing level valley bottom.WEDNESDAY: Cloudy, snow increasing. Accumulation 5-15 cm. Ridge wind strong, west. Temperature -3. Freezing level 1400 m.THURSDAY: Snow. Accumulation 15-25 cm. Ridge wind light, northeast. Temperature -14. Freezing level valley bottom.FRIDAY: Sunny. Ridge wind light, northeast. Temperature -16. Freezing level valley bottom.

Avalanche Summary

Monday natural wind slab activity up to size 1.5 was reported on steep, north-east facing features. Ski cuts and explosive control work produced several storm slab results (size 1.5-2) on north-east through south-east aspects between 1400-1600 m where the late January crust is present.On Saturday the east facing Mt. Corrigan slidepath produced a very large, natural avalanche. The avalanche is estimated to be a size 4.0, and it took out mature timber in the path as it overran the Flathead FSR south of Corbin. Also on Saturday, several 20-50 cm thick storm slabs were triggered with explosives at treeline elevations. A few natural cornice falls occurred on north and east aspect, one triggering a size 2 storm slab on the slope below.Early last week, many large (size 2-3) avalanches were triggered naturally and with explosives. Most of the natural avalanches were triggered by cornices falling and releasing slabs on the December and November layers, producing 150-250 cm thick crowns.

Snowpack Summary

The Fernie area experienced warm temperatures Saturday morning followed by a sudden drop to frigid temperatures in the afternoon. The results was a new surface crust that is now buried 20-50 cm at elevations below 1700 m. Areas closer to the divide likely stayed cold with low density snow. Higher elevations throughout the region stayed cold and windy, allowing the growth of touchy wind slabs and cornices.For the past month there has been regular avalanche activity on multiple deep weak layers. A layer buried mid-January is composed of surface hoar on sheltered aspects (especially prominent from 1400-1900 m) and a sun crust on solar aspects and is 60-80 cm deep. Another surface hoar layer from early-January is 90-110 cm deep. A widespread weak layer from mid-December composed of facets, crusts, and surface hoar is 120-160 cm deep. Finally, a rain crust with sugary facets buried in late-November is near the base of the snowpack.The bottom line is the snowpack structure is weak. Human triggering is most likely on the shallower weak layers, however a release near the surface also has the potential to step down to deeper layers and become a much larger avalanche.

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.