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Avalanche Forecast

Archived

Jan 12th, 2019–Jan 13th, 2019

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

Regions

North Columbia.

Warm air and sunny skies have arrived at higher elevations. The amount of warming and its influence on the snowpack is uncertain. Travel conservatively and observe for signs of snowpack warming -- conditions may change rapidly over the day.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

SATURDAY NIGHT: Partly cloudy skies, inversion conditions with above-freezing layer between 1700 m and 2500 m.SUNDAY: Clear skies, light southwest winds, alpine temperature -1 to 1 C, inversion conditions with above-freezing layer between 1700 m and 2400 m.MONDAY: Clear skies, light west winds, alpine temperature -1 to 3 C, inversion conditions with above-freezing layer between 1700 m and 2500 m.TUESDAY: Clear skies, light southwest winds, alpine temperature -1 C, freezing level dropping to below valley bottom.

Avalanche Summary

A few storm slab avalanches were triggered naturally, by skiers, and by explosives on Friday. They were small to very large (size 1 to 3.5), on all aspects, and generally at treeline and alpine elevations. See here for a recent report.For the weekend, the likelihood of triggering storm slabs may increase due to the substantial amount of warming expected around upper below treeline, treeline, and alpine elevations. Also watch out in thin snowpack areas, where the likelihood of triggering deeper layers is the highest. See here for a recent example.

Snowpack Summary

Warm upper-level air temperatures and sunny skies 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 produce touchy storm slabs at all elevations and particularly touchy on south aspects if the sun is strong. At the highest of elevations, wind slabs may still linger in lee and cross-loaded terrain features.The middle and lower portions of the snowpack are generally well-settled and strong. However, there still remain a few deeper weaknesses in the snowpack around treeline and alpine elevations. Professionals are still tracking a layer around 150 to 200 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. These layers would most likely be triggered by humans in areas where the snowpack is shallow. The likelihood of triggering these layers may increase with the warm air expected to last until Tuesday.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.