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Avalanche Forecast

Archived

Jan 16th, 2020–Jan 17th, 2020

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

Regions

Lizard-Flathead.

Expect fresh storm slabs from overnight snowfall. New snow may be sensitive to solar triggering on steep south-facing slopes if the sun comes out.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

Thursday night: Scattered flurries bringing 10-15 cm of new snow. Light to moderate southwest winds. Alpine temperatures around -7 C.

Friday: Mix of sun and cloud. Moderate west to southwest winds. Alpine high around -10 C.

Saturday: Mix of sun and cloud with scattered flurries bringing around 5 cm of new snow. Light to moderate southwest winds. Alpine high around -6 C.

Sunday: Mix of sun and cloud with scattered flurries bringing a trace of new snow. Moderate southwest winds. Alpine high around -3 C.

Avalanche Summary

Reports of avalanche activity over the past couple weeks have been steady, with each substantial snowfall accompanied by storm slab activity. Reports since Monday consist of explosive and skier controlled storm slab avalanches mostly around size 1.5, with some explosive triggered size 2. These MIN reports from last weekend describe natural storm slab avalanche activity including a cornice triggered size 2 storm slab.

Snowpack Summary

As temperatures trend milder, the new snow will take on more soft slab character than the unconsolidated fluff we were seeing in previous days. In the alpine, the new snow rests on wind affected surfaces. Expect freshly wind loaded pockets in lee features and continued cornice growth.

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 for several weeks.

Terrain and Travel

  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Brief periods of sun could quickly initiate natural avalanche activity.
  • Don't let the desire for deep powder pull you into high consequence terrain.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.