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Avalanche Forecast

Archived

Jan 27th, 2020–Jan 28th, 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.

Ongoing flurries and wind maintain wind slabs as a concern on Tuesday. Seek out sheltered slopes and watch for reactive pockets around steep rolls and ridge features.

Confidence

High - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

Monday night: Cloudy, isolated flurries, light to moderate southwest winds, alpine temperature -5 C.

Tuesday: Mix of sun and cloud, a trace of new snow, light to moderate southwest winds, alpine high temperature -2 C, freezing level around 1300 m.

Wednesday: Mix of sun and cloud, moderate southwest winds, alpine high temperature -2 C, freezing level around 1300 m.

Thursday: Mostly clear, light southwest winds, alpine high temperature -1 C, freezing level around 1500 m.

Avalanche Summary

Over the past several days, there have been reports of natural, human-triggered, and explosive triggered avalanches up to size 2.5 breaking in the new storm snow, specifically where it has been drifted by wind into stiffer slabs on northwest through northeast aspects. A couple of these avalanches have been reportedly triggered by cornice fall.

Snowpack Summary

Southwest winds have drifted 20-30 cm of recent snow into slabs on lee and cross-loaded terrain features at upper elevations. This combination has also contributed to cornice growth, increasing the need for vigilance with overhead hazard. A temperature crust formed Friday at least as high as 1600 m.

The stout upper snowpack continues to settle in mild temperatures. Several crust layers exist in the mid-pack 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 the region since December.

Terrain and Travel

  • Be alert to conditions that change with elevation, aspect and exposure to wind.
  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • 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.