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Avalanche Forecast

Archived

Feb 4th, 2020–Feb 5th, 2020

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

Regions

Lizard-Flathead.

Triggering wind slab avalanches is possible in steep open terrain.

Confidence

High - The number, quality, or consistency of field observations is good, and supports our confidence.

Weather Forecast

TUESDAY NIGHT: Cloudy with light flurries, moderate wind from the west, alpine temperatures drop to -12 C.

WEDNESDAY: Scattered flurries with 5-10 cm of low density snow, moderate wind from the west, alpine high temperatures around -8 C.

THURSDAY: Cloudy with isolated flurries, light wind from the west, alpine high temperatures around -5 C.

FRIDAY: Mix of sun and cloud with storm approaching in the evening, light wind, alpine high temperatures around -5 C.

Avalanche Summary

A large cornice fall was reported on Tuesday, and fragile cornices were also observed on Monday. A few small (size 1) wind slabs were triggered by riders on north aspects on Sunday. A widespread natural avalanche cycle on Friday night resulted in large (size 2-3) storm slab, wet slab, and wet loose avalanches. Reports suggest deeper weak layers were not involved in these avalanches.

With a crust capping the snowpack in most areas, the main concern is now small stubborn wind slabs above the crust.

Snowpack Summary

Strong southwest winds have likely formed isolated wind slabs in the alpine and exposed treeline areas above 2100 m. Below this elevation, 5-10 cm of snow, also wind-affected, covers a solid melt-freeze crust that now caps the mid and lower snowpack. In many areas this capping crust may extend to mountaintops.

The bottom 10-20 cm of the snowpack consists of faceted snow and decomposing crusts. This basal layer has not been an active avalanche problem in the region since December and would likely require a sustained warming event before re-emerging as a concern.

Terrain and Travel

  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Use caution above cliffs and terrain traps where even small avalanches may have severe consequences.

Problems

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.