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Avalanche Forecast

Archived

Jan 29th, 2021–Jan 30th, 2021

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

Regions

Lizard-Flathead.

The new snow formed reactive storm slabs at all elevations. The slabs are particularly reactive where they overlie surface hoar. Moderate southwest wind will build fresh wind slabs at higher elevations throughout the day.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

FRIDAY NIGHT: Cloudy with clear periods, up to 5 cm new snow, light to moderate southwest wind, treeline temperature -7 C.

SATURDAY: Cloudy, 5 cm new snow, moderate southwest wind, treeline temperature -6 C.

SUNDAY: Cloudy, 10 cm new snow, moderate southwest wind, treeline temperature -4 C.

MONDAY: Cloudy, 15-20 cm new snow, moderate southerly wind, treeline temperature -2 C.

Avalanche Summary

A skier triggered size 2 slab avalanche was reported on Friday (see this valuable MIN post). Several slab avalanches up to size 2 released naturally and were triggered by explosives on Thursday. Other parties reported signs of instability as whumpfing and shooting cracks. Loose dry avalanches (sluffs) in steep alpine and treeline features were observed in the last few days. 

Snowpack Summary

20-30 cm recent snow buried surface hoar and other old surfaces. In the alpine, the new snow sits on top of layers of hard wind slab, scoured areas, sastrugi and isolated pockets of soft snow. A hard crust underneath the new snow is found up to 1800 m.    

A solid mid-pack sits above a deeply buried crust and facet layers near the bottom of the snowpack (150-200 cm deep), which are currently unreactive. 

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Be carefull with sluffing in steep terrain, especially above cliffs and terrain traps.

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.