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Avalanche Forecast

Archived

Mar 15th, 2012–Mar 16th, 2012

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

Regions

Northwest Inland.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Friday: Light snowfall - light southwest winds - freezing level at 800m Saturday: very light snowfall with a chance of intermittent sun - light and variable winds increasing in the evening freezing level at 600m Sunday: scattered cloud - light and variable winds - freezing level at 500m

Avalanche Summary

Sluffing in steep terrain was observed on Wednesday. Observations from the region have been very limited.

Snowpack Summary

Moderate amounts of low density snow sit over a variety of old surfaces that include widely distributed hard wind slabs, or melt freeze crusts that exist on most aspects below 1000m and on solar aspects as high as 1600m. In exposed areas the newer snow has been shifted into deeper pockets of soft wind slab. The mid February persistent weak layer interface, comprised of spotty surface hoar, facets and crusts, is buried approximately 80cm below the surface. No recent activity has been reported on this interface, but it should still be on your radar, particularly in steeper, unsupported terrain. Cornices in the area are also reported to be very large and primed for triggering.

Problems

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.

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.

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.