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Avalanche Forecast

Archived

Mar 7th, 2020–Mar 8th, 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.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Lizard-Flathead.

Start small and watch for signs of instability or indications that new snow has settled into a reactive slab over the old snow surface on Sunday. Expect new snow to become especially touchy on southerly slopes if the sun makes an appearance.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Saturday night: Cloudy with continuing flurries bringing 5-10 cm of new snow. Moderate southwest winds. 

Sunday: Mainly cloudy with isolated flurries and a trace of new snow. Moderate to strong southwest winds. Alpine high temperatures around -9.

Monday: Sunny. Light southwest winds. Alpine high temperatures around -8.

Tuesday: Mainly sunny in the morning with cloud increasing over the day. Moderate to strong southwest winds. Alpine high temperatures around -4.

Avalanche Summary

Preliminary reports from Saturday mainly show new snow reacting to skier traffic and explosives control as dry loose sluffs, reaching size 2. Soft slab formation was noted in wind-affected features at ridgecrest. 

Elevated avalanche danger is expected to be maintained through Sunday as the new snow settles into more consolidated storm slabs that only gradually begin bonding with the previous snow surface. Periods of sunshine may also promote natural avalanche activity.

Snowpack Summary

By the time snowfall eases off Saturday night, new snow totals over the region may reach up to 30 cm. The new snow has buried heavily wind affected surfaces in exposed areas as well as sun crust on solar aspects and temperature crusts up to 1700 m on all other aspects. The new snow is not expected to bond well with any of these surfaces over the short term.

A thick rain crust that has facets associated with it sits 30-60 cm below the surface and can be found up to ridgetops. We have only seen one avalanche on this layer since February 17th. The mid-pack is well settled and strong, but the base of the snowpack contains basal facets that are most prominent in shallow rocky start zones.

Terrain and Travel

  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Make conservative terrain choices and avoid overhead hazard.

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.