Avalanche Forecast

Archived

Mar 8th, 2013–Mar 9th, 2013

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

South Coast.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Sunday

Weather Forecast

A ridge of high pressure should persist for one more day bringing mainly clear skies for Saturday. Winds are expected to be light and northwesterly with the freezing level at 1900m.The ridge then flattens and a more zonal pattern is forecast to bring snowfall and seasonal temperatures to the region for Sunday and Monday. At this point there is significant model disagreement with the timing and intensity of this next system.

Avalanche Summary

Sun forecast for Saturday could trigger loose wet avalanche activity on steep solar features. Warming also has the potential to trigger cornice releases or deeper persistent slab avalanches in isolated terrain.

Snowpack Summary

Light amounts of recent snowfall sit on 60-100 cm of settling storm snow from last week. Below 1400m in the north and 1700m in the south the light amounts of new snow overlie a thick rain crust. These recent accumulations may also exist as wind slabs in exposed terrain.At the base of last week's storm snow is a layer of buried surface hoar (February 20th). This layer was the culprit in most of the large avalanches that occurred last weekend. Snowpack tests continue to show sudden planar results and good potential for propagation. Triggering this layer is becoming more difficult, but I recommend avoiding any large slopes that did not release during the last cycle, especially when the sun pokes out this weekend. Below this the snowpack is generally well settled and strong.

Problems

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.

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.