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Avalanche Forecast

Archived

Mar 17th, 2022–Mar 18th, 2022

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

North Rockies.

Buried weak layers continue to be a concern. Stick to conservative terrain with minimal overhead hazard and watch for signs of instability like whumpfing, natural avalanches and cracking. Find more information on this tricky layer here.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

THURSDAY NIGHT: Flurries continue overnight, with freezing levels dropping to valley bottom. Moderate west-southwest winds. 

FRIDAY: A mix of sun and cloud, isolated flurries. Freezing level rising to 1600 m. Alpine high of 0. Moderate southwesterly winds. 

SATURDAY: Partly cloudy, light flurries. Freezing levels reach 1800 m. Moderate southerly winds turn west in the afternoon. Alpine high of +2.

SUNDAY: Around 5 cm possible overnight. Mostly sunny with moderate southwest winds. Freezing levels reaching 1500 m. Moderate southwest winds. Alpine high of -2.

Avalanche Summary

On Wednesday, explosive control south of Renshaw produced avalanches up to size 3 within the recent storm snow. Loose wet activity was triggered at lower elevations to size 2.5.

Natural activity was observed in specific wind loaded features around ridgelines to size 1.5.

Last weekend, numerous natural and sledder-triggered avalanches were reported in the Pine Pass and Renshaw area, all failing on surface hoar. The most reactivity has occurred on wind-loaded, northeast aspects. Most notably, a size 2.5 sledder-triggered avalanche occurred near Bijoux Falls. The full report can be seen here.

Snowpack Summary

40-80 cm of settling storm snow is being redistributed into wind loaded features at higher elevations. At lower elevations moist snow or a melt-freeze crust likely exists from recent rain and warm temperatures.

This new snow is sitting on various surfaces, including hard wind-affected snow, sun crusts on southerly slopes, and large surface hoar on shaded and sheltered slopes. This layer of surface hoar is expected to remain reactive, with the most activity observed in the Pine Pass and Renshaw area.

The mid and lower snowpack is generally well-settled and strong in most areas, with multiple crusts throughout. 

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Carefully monitor the bond between the new snow and old surface.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

Problems

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.

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.