Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Feb 16th, 2020–Feb 17th, 2020

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

Regions

Lizard-Flathead.

Storm slabs will likely remain sensitive to human triggering especially in deep wind-loaded pockets in alpine lees. Fresh snow will shed easily from steep slopes that see periods of direct sun exposure Monday.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

Sunday night: Clear periods with possible flurries. Light northwest winds. Alpine low -12 C. Freezing level valley bottom.

Monday: Mix of sun and cloud with possible flurries. Light northwest winds. Freezing level 900 m.

Tuesday: Mix of sun and cloud. Light northwest winds. Freezing level valley bottom.

Wednesday: Sunny. Light northwest winds. Freezing level 700 m.

Avalanche Summary

Explosive control work conducted on Sunday produced mostly loose avalanches up to size 1.5 with limited slab property in storm snow. Reports from Saturday consisted of small (size 1) natural cornice/slab and skier triggered wind slab avalanches. On Friday, several natural and explosive triggered storm slabs reached size 2, with crown fracture depths of 20-40 cm. Wind-loaded northeast aspects above 1900 meters featured most prominently. Several natural cornice falls were another stand-out feature.

Snowpack Summary

20-30 cm of snow from the past week has been blown into wind slabs and cornices. In sheltered areas, the recent snow is settling and may contain sun crusts and layers of surface hoar. 

A thick rain crust sits 30-60 cm below the surface, up to 2100 m. Recent reports indicate that faceting may be occurring at the interface of this crust and overlying snow in some areas. A weak layer sitting between a dense slab and a slick bed surface is a recipe for a future persistent avalanche problem.

The bottom 20 cm of the snowpack consists of basal facets and decomposing crusts that have not been an active avalanche problem since December, but could reemerge as a problem after sustained warming.

Terrain and Travel

  • Seek out sheltered terrain where new snow hasn't been wind-affected.
  • Caution around slopes that are exposed to cornices overhead.
  • Be alert to conditions that change with elevation and sun exposure.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.