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Avalanche Forecast

Archived

Mar 18th, 2020–Mar 19th, 2020

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

Regions

North Rockies.

Persistent slabs remain a concern at lower elevations. Observations will decrease as folks retreat to low-risk activities and social distancing. Be sure to keep risk tolerance to a minimum if you're heading out and to share your observations on the Mountain Information Network.

Confidence

Moderate -

Weather Forecast

Wednesday night: Clear. Light east or northeast winds.

Thursday: Sunny. Light east or northeast winds. Alpine high temperatures around -8.

Friday: Sunny. Moderate west winds. Alpine high temperatures around -4.

Saturday: A mix of sun and cloud. Light north winds. Alpine high temperatures around -10.

Avalanche Summary

No new avalanches were reported over the past couple of days, however a natural wind slab avalanche cycle up to size 2.5 (large) was observed on Saturday. One size 3 (very large) was reported on a south aspect as well. No avalanches were reported at lower elevations where surface hoar is known to exist but where observations are scarce.

Looking forward, the possibility for human triggering of isolated wind slabs at upper elevations is now likely limited to very steep terrain at ridgecrest. At lower elevations, human triggering of avalanches remains possible where slabs have formed over persistent weak surface hoar layers.

Snowpack Summary

Recent sunshine has been strong enough to create a new surface crust on steep southerly slopes, thickest at lower elevations. Recent wind slabs are expected to be on a positive stabilizing trend.

At lower elevations, two surface hoar layers 50-60 cm and 75-90 cm below the surface remain a concern - especially where a slab has formed on the surface from warming and/or winds over the weekend. 

Terrain and Travel

  • Be very cautious in open terrain features, such as cutblocks, gullies, and cutbanks.
  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.

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.