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Avalanche Forecast

Archived

Feb 19th, 2022–Feb 20th, 2022

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

Regions

Lizard-Flathead.

Keep terrain selection conservative as storm snow accumulates, expect the new snow to bond poorly to old snow surfaces.

Avoid avalanche terrain and exposure to overhead hazard during peak snowfall.

Confidence

Moderate - We are confident a natural avalanche cycle will begin shortly after the arrival of the incoming weather. Forecast snowfall amounts are uncertain.

Weather Forecast

SATURDAY NIGHT: 10-15 cm by morning. Freezing levels drop to valley bottom. Winds ease to moderate from the east.

SUNDAY: Snowfall continues with another 10-20 cm of snow possible over the day, light northeast winds. Freezing levels at valley bottom. Alpine high of -20. 

MONDAY: Mostly sunny, moderate wind from the northeast. Freezing levels below valley bottom, alpine high of -20. Chance of isolated flurries. 

TUESDAY: Mostly clear, moderate northeast winds. Freezing levels below valley bottom. Alpine high of -20. 

Avalanche Summary

Avalanche activity over the past few days has been limited to small slabs and loose avalanches in steep alpine terrain. 

With the incoming storm we expect to see natural and human triggered avalanche activity increase. 

Snowpack Summary

Up to 40 cm of new snow by Sunday afternoon will form reactive storm slabs at all elevations. The storm snow will bury a melt freeze crust on solar aspects at all elevations, and wind affected surfaces in exposed terrain. 

A buried surface hoar layer can be found 30-60 cm deep on north-facing slopes around treeline. This layer has been reactive in snowpack tests, and new snow is expected to increase the likelihood of triggering this layer. 

The snowpack below is well consolidated, with a crust/facet layer found near the bottom of the snowpack. It is currently considered dormant, but could become active later this season. Check out the forecaster blog for more information. 

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy snowfall.
  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.