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Avalanche Forecast

Archived

Mar 29th, 2013–Mar 30th, 2013

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

Regions

Purcells.

The region will be under the influence of a major warm-up through the weekend.  Be aware of snow conditions changing quickly and avalanche danger increasing.

Confidence

Good

Weather Forecast

The region continues to be under a significant high pressure system and blocking pattern that will not allow any active weather throughout the forecast period. Sunny skies with few clouds and unseasonable high freezing levels will continue.Saturday: Few clouds. Alpine temperatures near 5.0 and freezing levels rising to 2500 m. Ridgetop winds will blow light from the West.Sunday: Mostly sunny with possible high cloud. Alpine temperatures 4.0 degrees and freezing levels 2600 m. Ridgetop winds will be light from the NW.Monday: Mix of sun and cloud. Alpine temperatures near 0.0 degrees and freezing levels hover around 2200 m. Ridgetop winds blowing light from the West.

Avalanche Summary

Several solar induced cornice releases up to size 3 occurred, not triggering slabs on the slopes below. Numerous  loose wet avalanches initiated from solar aspects above 2000 m up to size 2.Expect this type of avalanche activity to persist through the forecast period.

Snowpack Summary

Surface faceting and surface hoar growth (up to 20 mm) has been prevalent on shady slopes and at upper elevations, while the surface snow on sun-exposed slopes and at lower elevations has been subject to daily melt-freeze cycles.Cornices are reported to be very large and weakly bonded. Cornice fall is ongoing. Wind and storm slabs are to be strengthening, but may continue to be sensitive to human-triggers. The weak layer of buried surface hoar sitting on a crust down around 70-120cm, and has been producing variable but sudden results in snowpack tests. This deep persistent weakness remains a concern because of the potential for very large avalanches particularly with heavy triggers such as cornice falls. Old deep persistent weaknesses, including basal depth hoar, are a concern in shallow snowpack areas.

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.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.