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Avalanche Forecast

Archived

Jan 12th, 2019–Jan 13th, 2019

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
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 unlikely, human triggered possible.

Regions

Purcells.

Warm air and sunny skies have arrived for most of the region. It may be more likely to trigger avalanches with these conditions. It is best to avoid alpine avalanche terrain and be very cautious at treeline until the temperature cools.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

FRIDAY NIGHT: Partly cloudy, inversion conditions with above freezing layer between 2000 m and 2500 m.SATURDAY: Partly cloudy, light southwest winds, alpine temperature variable between -1 and 3 C, inversion conditions with above freezing layer between 1800 m and 2800 m.SUNDAY: Clear skies, light southwest winds, alpine temperature 3 C, inversion conditions with above freezing layer between 1600 m and 2800 m.MONDAY: Clear skies, light southwest winds, alpine temperature 3 C, inversion conditions with above freezing layer between 1600 m and 2800 m.

Avalanche Summary

On Friday, five more deeply buried weak layers released and formed large to very large avalanches (size 2 to 3.5). They were triggered naturally, by skiers, and by explosives and released on northeast, north, and west aspects, between 2300 and 2700 m, and inclines over 35 degrees. They likely released within the weak layers described in the snowpack summary. Otherwise, numerous wind and storm slab avalanches also released small to large avalanches (size 1 to 3), on all aspects and generally in alpine terrain.On Thursday, small to large (size 1 to 2) storm slab and wind slab avalanches were triggered naturally and by skiers. They were generally at treeline and alpine elevations and on all aspects. A natural avalanche, likely on the layer buried 80 to 120 cm, released in the alpine from very steep terrain.For the weekend, the likelihood of triggering avalanches may increase due to the substantial amount of warming expected around upper below treeline, treeline, and alpine elevations. Watch out in thin snowpack areas, where the likelihood of triggering deeper layers is the highest. Check out recent large and destructive avalanches triggered by people via MIN posts here and here.

Snowpack Summary

Warm upper-level air temperatures may be impacting the snow surface. You may find dry snow, moist snow, or possibly a frozen melt-freeze crust, depending on how warm the air temperatures are. The warm air may make slabs touchy at all elevations.Of concern are the deeper weaknesses in the snowpack. There is a weak layer around 80 to 120 cm deep, composed of sugary faceted grains, feathery surface hoar, and a sun crust. The base of the snowpack may also still be composed of weak faceted grains. Humans could trigger these layers in areas where the snowpack is shallow. The likelihood of triggering these layers may increase this weekend due to a substantial warming trend.

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.