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Avalanche Forecast

Archived

Feb 16th, 2018–Feb 17th, 2018

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

Regions

Sea To Sky.

Southern parts of the region near Squamish may get enough snow for HIGH danger. Prepare to scale back your terrain choices if you see heavy snowfall or blowing snow in your local area.

Confidence

Moderate - Track of incoming weather systems is uncertain

Weather Forecast

SATURDAY: Moderate snowfall with 15-30 cm throughout the day, strong southwest wind, freezing level up to 800 m with alpine high temperatures around -7 C.SUNDAY: Clearing and cooling with moderate northeast wind and alpine high temperatures around -15 C.MONDAY: Mostly sunny, light northeast wind, alpine high temperatures around -15 C.

Avalanche Summary

On Friday, several small storm slabs (size 1) were reactive below ridgetops and other wind-loaded slopes at treeline and alpine elevations.Several large cornices collapses were reported last week. One resulted in a fatal accident in the Callaghan area on Saturday. A snowmobiler was parked 7-10 m back from the edge of a corniced ridge when a large chuck broke off and took the rider down the slope. See here for a full report. A similar incident occurred nearby the same day, but the person only suffered minor injuries. Fragile cornices continue to be a concern in the region.

Snowpack Summary

15-30 cm of new snow is expected to form fresh storm slabs on Saturday. The new snow is burying hard wind-affected snow in exposed terrain, a hard crust below 1900 m, and a sun crust on south-facing alpine slopes. The mid-January crust is now buried beneath 150-200 cm of settled snow, but a heavy trigger such as a cornice fall could potentially wake up this layer. The lower snowpack is generally strong and well-settled.

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.