Avalanche Forecast

Archived

Feb 15th, 2018–Feb 16th, 2018

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural and human triggered avalanches likely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

South Coast.

New snow sits above a hard crust. Be careful around terrain traps such as cliffs, trees, or gullies where a small avalanche could have severe consequences.

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

FRIDAY: 5-10 cm of new snow by the morning then clearing throughout the day, moderate west wind, freezing level climbing to 900 m with alpine high temperatures around -2 C.SATURDAY: Heavy snow starting Friday night with 30-40 cm possible by the end of the day, strong southwest wind, freezing level around 800 m with alpine high temperatures around -2 C. SUNDAY: Some isolated flurries with clearing throughout the day, strong northeast wind, freezing level dropping with alpine high temperatures around -6 C.

Avalanche Summary

Storm snow was reactive above the crust on Wednesday. Numerous size 1-2 skier and naturally triggered slabs were reported on various aspects at treeline. See here for an example. A cornice collapse was the likely cause of a size 2 avalanche on a north facing slope near the West Lion last weekend. See here for images and more details. Given the poor bond between the new snow and the crust, expect storm slabs to remain reactive for the next few days.

Snowpack Summary

Storm snow is accumulating above a hard rain crust that extends into alpine terrain. By Friday afternoon there could be 30 cm of snow above the crust, enough to make reactive slabs in steep terrain. Deeper wind deposits are likely in alpine terrain. The average snow depth at treeline is 300 cm, with no layers of concern in the lower snowpack.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.