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Avalanche Forecast

Archived

Mar 12th, 2018–Mar 13th, 2018

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

Regions

Lizard-Flathead.

Freezing levels well above the mountain tops and sunny skies are intensely warming the snowpack, particularly around midday. Best to avoid areas with sun exposure, wind effect, and overhead avalanche terrain. Read our blog on the impact of warming.

Confidence

High -

Weather Forecast

TUESDAY: Sunny, light southwesterly winds, alpine temperature 4 C, freezing level 3000 m.WEDNESDAY: Mix of sun and cloud, light southwesterly winds, alpine temperature 3 C, freezing level 2500 m.THURSDAY:  Mostly cloudy with light snowfall, accumulation 5 cm, light westerly winds, alpine temperature 0 C, freezing level 1500 m.

Avalanche Summary

Numerous wind and wet slabs to size 2 were reported in the region on Sunday, being triggered naturally and by large triggers.  The wet slabs were on southerly aspects in the alpine and the wind slabs were on a northwesterly aspect.  Small loose avalanches to size 1.5 were observed on solar aspects.  Two natural cornice falls were also noted on alpine ridges.The forecast warming and sunshine may wake up a deeper weak layer on steep south facing slopes resulting in large and destructive avalanches.

Snowpack Summary

Warm air temperatures and daytime sun have produced moist snow on solar aspects into the alpine and moist snow on all aspects up to 1400 m.  On shady aspects at higher elevations, expect to find wind slabs in lee features and loose dry in sheltered features.  These snow surfaces are sitting on patchy surface hoar in parts of the region.Cornices are large and prone to failure with warm air temperatures and sunny skies.In the upper to mid snowpack, a surface hoar or facet layer buried mid-February is 80 to 110 cm below the surface on sheltered northerly aspects.Deeper in the snowpack, the widespread mid-December and late November weak layers are composed of a combination of crusts and sugary facets which are down 200-300 cm. These layers have been dormant but may be awoken by the warm and sunny weather throughout the weekend or by a large trigger, such as a falling cornice.

Problems

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.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.