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Avalanche Forecast

Archived

Jan 13th, 2021–Jan 14th, 2021

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 unlikely, human triggered possible.
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

North Rockies.

New snow and wind Tuesday night has create new fresh and reactive wind slabs at upper elevations. There is still uncertainty with a persistent slab problem that seems to be most prevalent in the Pine Pass area. 

Confidence

Moderate - Uncertainty is due to field data and reports showing a wide variation in conditions throughout the region.

Weather Forecast

WEDNESDAY NIGHT: Cloudy with flurries, moderate west and northwest wind, alpine temperature -7 C, freezing level 500 m.

THURSDAY: Mix of sun and cloud, light west wind, alpine temperature -8 C.

FRIDAY: Mainly cloudy with scattered flurries, accumulation 3-5 cm, moderate to strong southwest wind, alpine temperature -5 C.

SATURDAY: Cloudy with isolated flurries, moderate west wind, alpine temperature -6 C, freezing level 1300 m.

Avalanche Summary

No recent avalanche activity has been noted. Expect to see an increase in wind slab activity on Thursday.

Snowpack Summary

Up to 15 cm of snow falling in the south and west of the region Tuesday night came with moderate to strong southwest wind. This sits on previously wind-affected snow in exposed areas, soft snow and perhaps surface hoar in sheltered areas, and a hard melt-freeze crust or moist snow below about 1600 m.

You may find a couple weak layers of surface hoar in the top 50 cm of the snowpack, as suggested by numerous MINs in the region. This layer is expected to be found in terrain features sheltered from the wind, for example in openings below treeline or at treeline elevations. As the new snow forms slab properties, these layers could become reactive to human traffic.

Around 80 to 100 cm of snow rests above a weak layer buried in early-December which has created a persistent slab avalanche problem and a low probability/high consequence scenario. Depending on location, the buried weak layer is composed of surface hoar and/or a crust/facet combination. Reports suggest that this layer has become dormant in much of the region except for perhaps the Pine Pass area.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.