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Avalanche Forecast

Archived

Feb 10th, 2021–Feb 12th, 2021

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

Regions

North Rockies.

Human triggered avalanches at treeline remain possible, but time and cold temperatures have reduced their sensitivity to triggering. Watch for wind slabs in funny places in the alpine as easterly winds continue to blow.

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

Brrrr! Cold temperatures look to be with us through the weekend. The weather models are hinting at more seasonal temperatures beginning Tuesday.

WEDNESDAY NIGHT: Overnight low temperature around -38 C, moderate northeast wind, no snow expected. 

THURSDAY: A few clouds, daytime high temperature around -20 C, moderate to strong east/southeast wind, no snow expected.

FRIDAY: A few clouds, daytime high temperature around -18 C, moderate to strong east/southeast wind, no snow expected.

SATURDAY: Clear skies at dawn with cloud cover steadily increasing through the day, daytime high temperature around -16 C, strong southeast wind, no snow expected.

Avalanche Summary

There were a few small human triggered avalanches reported around treeline near Pine Pass last weekend. 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 February 3rd 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

  • Be careful as you transition into wind affected terrain.
  • Avoid open slopes and convex rolls at and below treeline 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.