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Avalanche Forecast

Archived

Mar 6th, 2020–Mar 7th, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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, human triggered possible.

Regions

Lizard-Flathead.

Avalanche danger will increase rapidly as heavy snowfall blankets the region through Saturday. Stick to simple terrain that is free of overhead hazards - and enjoy the new snow!

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Friday night: Cloudy with increasing flurries bringing about 10 cm of new snow. Light to moderate southwest winds.

Saturday: Cloudy with continuing heavy snowfall bringing 15-25 cm of new snow. Moderate to strong south winds. Alpine high temperatures around -5.

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

Monday: A mix of sun and cloud. Light to moderate southwest winds. Alpine high temperatures around -8.

Avalanche Summary

A few small loose avalanches were observed on sun-exposed slopes on Tuesday and Wednesday. Over the weekend a few small wind slab avalanches (see this MIN report) and size 2 cornice falls were reported. The cornice falls did not trigger any slabs on the slopes below.

Looking forward, heavy snowfall over Friday night and Saturday is expected to rapidly increase avalanche danger in the region as it accumulates and forms new storm slabs that bond poorly with the current snow surface.

Snowpack Summary

Up to 35 cm of new snow is expected to accumulate in the region by the end of the day on Saturday. The new snow will bury 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 near 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

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • 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.