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Avalanche Forecast

Archived

Mar 21st, 2016–Mar 22nd, 2016

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

Conditions may change quickly in the spring. Even brief periods of sun can trigger pushy loose wet avalanches or promote destructive cornice falls.

Confidence

High

Weather Forecast

On Tuesday expect generally overcast skies with isolated flurries. On Wednesday a Pacific system will bring 5-15cm of new snow to the region. Light flurries are forecast for Thursday. Ridgetop winds will be light on Tuesday, and then become moderate and southeasterly with Wednesday's precipitation. Freezing levels should hover between 1100 and 1200m for the forecast period.

Avalanche Summary

No recent avalanches have been reported.

Snowpack Summary

Light amounts of new snow have been shifted by strong southeast winds into wind slabs in exposed high elevation terrain while settled powder can be found on shaded and sheltered slopes. Spring conditions have continued to develop. With that, lower elevation and sun-exposed slopes will likely appear moist or refrozen. A layer of surface hoar or melt-freeze crust buried on March 3 is down 50-80cm and has been on the radar of professionals in the mountains north of Stewart. A more widespread crust/facet layer buried in early February can now be found down over a meter. Both of these deeper layers have become less likely to trigger, but have the potential for large avalanches especially with a large trigger such as a cornice fall. I'd be increasingly cautious during periods of warming or solar radiation.

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.

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.