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Avalanche Forecast

Archived

Feb 8th, 2021–Feb 9th, 2021

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

Regions

North Rockies.

Bundle up! A true arctic outbreak is upon us.

If you'd rather brave the cold than cozy up to a wood stove, then keep in mind that a persistent weak layer may continue to be reactive, in spite of the frigid weather. The layer is most prominent around treeline. 

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

MONDAY NIGHT - Mainly cloudy with clear periods / light northwest wind / alpine low temperature near -33 

TUESDAY - A mix of sun and cloud with isolated flurries / light southeast wind / alpine high temperature near -27

WEDNESDAY - A mix of sun and cloud with isolated flurries / moderate northeast wind / alpine high temperature near -28

THURSDAY - Mainly sunny / strong to extreme northeast wind / alpine high temperature near -30

Avalanche Summary

There were a few small human triggered avalanches reported around treeline near Pine Pass on Sunday. These failed on the recently buried surface hoar layer. 

There were some other observations from throughout the region over the weekend that would suggest ongoing instability associated with that weak surface hoar layer. Reports ranged from whumpfs and shooting cracks, to visual observations of large surface hoar crystals

On Wednesday and Thursday wind slab development was noted in the Kakwa, more details and images here.

On Wednesday there were reports of numerous natural avalanches 20 to 40 cm in depth running at and above treeline. A southwest slope produced a size 3 natural avalanche. These avalanches presumably ran on surface hoar which was producing very touchy conditions. There are some great visuals of this activity in this MIN.

Snowpack Summary

There is about 40-80 cm of snow resting on buried surface hoar which is most prevalent above 1600 m. It likely reaches into the alpine too, we're just not sure how high it extends.

Below 1600 m this snow sits on a crust. 

There are presently no deeper concerns in the snowpack.

Terrain and Travel

  • Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Be careful as you transition into wind affected terrain.

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.