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Avalanche Forecast

Archived

Jan 13th, 2019–Jan 14th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Warm air and sunny skies may deteriorate the snowpack. Observe for signs of snowpack warming, travel conservatively, and expect rapid changes over the day.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

SUNDAY NIGHT: Clear skies, inversion conditions with above-freezing layer between 1800 m and 2300 m.MONDAY: Clear skies, light southwest winds, alpine temperature 1 to 3 C, inversion conditions with above-freezing layer between 1700 m and 2800 m.TUESDAY: Clear skies, light southwest winds, alpine temperature 0 C, inversion conditions with above-freezing layer between 2000 m and 2500 m.WEDNESDAY: Mostly clear skies, light southwest winds, alpine temperature -5 C, freezing level below valley bottom.

Avalanche Summary

Numerous storm and wind slab avalanches were observed in the region on Saturday. They were small to large (size 1 to 2), in alpine terrain, and generally on northerly aspects. They were triggered naturally, by skiers, and explosives. See here for a recent report. Naturally-triggered loose avalanches were also observed, generally out of steep terrain.For the weekend, the likelihood of triggering slab avalanches 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 air temperatures and sunny skies may impact the snow surface at higher elevations. You may find dry or moist snow, depending on how warm it gets. On south aspects, you will likely find moist snow during the day or a sun crust if it freezes. The warm air may increase the reactiveness of storm slabs, particularly on southerly aspects where the greatest amount of warming is expected. Wind slabs may still linger in lee and cross-loaded terrain features in alpine and exposed treeline terrain.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 people 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

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.

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.