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Avalanche Forecast

Archived

Jan 21st, 2020–Jan 22nd, 2020

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

Regions

Lizard-Flathead.

Carefully evaluate bigger alpine lines for pockets of wind slab sensitive to human triggering. After Wednesday, the freezing level will start to creep higher.

Confidence

Moderate - Uncertainty is due to difficult to forecast freezing levels. Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Tuesday night: Overcast with isolated flurries bringing around 5 cm of new snow. Moderate southwest winds, strong at ridgetop. Alpine low -5 C. Freezing level around 1000 m.

Wednesday: Broken cloud with isolated flurries bringing up to 5 cm of new snow. Moderate southwest winds. Alpine high -4 C. Freezing level around 1200 m.

Thursday: Broken cloud with isolated flurries bringing a trace of new snow. Moderate west to southwest winds, strong at ridgetop. Alpine high -1 C. Freezing level rising to 1600 m.

Friday: Broken cloud with isolated flurries bringing up to 5 cm of new snow. Moderate west to southwest winds, strong at ridgetop. Alpine high 0 C. Freezing level rising to 1800 m.

Avalanche Summary

On Monday, natural storm slabs up to size 1.5 were observed in steep alpine terrain below cliffy headwalls in the Lizard range. One was triggered by a cornice fall. 

Over the weekend, results from control work were also limited to size 1.5. A natural storm cycle occurred Friday size 1.5-2.5.

Snowpack Summary

Thin surface crusts may be found on a variety of aspects and elevations. Wind loaded pockets are forming in lee features in the alpine. After over 1 m of steady snowfall last week, the stout upper snowpack continues to settle in the mild temperatures. 

Several crust layers exist in the mid snowpack as a result of previous warming and rain events. These have not been identified as bed surfaces or failure planes in recent avalanche activity.

The bottom 10-20 cm of the snowpack consists of faceted snow and decomposing crusts. Although inherently weak, this basal layer has not been an active avalanche problem in our region since 2019.

Terrain and Travel

  • Carefully evaluate bigger terrain features on an individual basis before committing to them.
  • 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.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.