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Avalanche Forecast

Archived

Jan 24th, 2020–Jan 25th, 2020

Alpine
Natural avalanches possible, human triggered probable.
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

Lizard-Flathead.

Pay attention if the sun comes out in the alpine on Saturday. New snow is especially sensitive to solar triggering.

Confidence

Moderate - Uncertainty is due to rapidly fluctuating freezing levels.

Weather Forecast

Friday night: 5-10 cm new snow. Moderate west to southwest winds. Freezing level around 1000 m.

Saturday: Cloudy with sunny breaks. A trace of new snow. Light west to southwest winds. Freezing level around 1400 m.

Sunday: Mostly cloudy. A trace of new snow. Light west to southwest winds. Freezing level around 1400 m.

Monday: Mostly cloudy. A trace of new snow. Moderate west to southwest winds. Freezing level around 1400 m.

Avalanche Summary

Over the last 3 days there have been numerous reports of natural storm slab activity up to size 2.5 on northeast aspects in the alpine. Explosive control work has been up to size 2, as well as reports of skier triggered size 1s.

Snowpack Summary

New snow and moderate southwest winds have formed wind slabs in lee features in the alpine. 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 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

  • Be alert to conditions that change with elevation, aspect and exposure to wind.
  • Be careful as you transition into wind affected terrain.
  • Even brief periods of direct sun could produce natural avalanches.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

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.