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Avalanche Forecast

Archived

Jan 6th, 2019–Jan 7th, 2019

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, human triggered possible.

Regions

South Coast Inland.

Monday brings a short break in the stormy weather, but storm slabs are still likely to be encountered and could be reactive to human triggering, especially in wind loaded areas.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain on Wednesday

Weather Forecast

SUNDAY NIGHT - Cloudy with clear periods and isolated flurries / southwest winds, 40-60 km/h / alpine low temperature near -10MONDAY - Cloudy with sunny periods / west winds, 40-50 km/h / alpine high temperature near -8TUESDAY - A mix of sun and cloud  / southeast winds, 15-20 km/h / alpine high temperature near -5 WEDNESDAY - Snow, 5-10 cm / southeast winds, 20-40 km/h / alpine high temperature near -5

Avalanche Summary

On Saturday, one natural size 2 avalanche was reported in the region on an east to north aspect at 1900 m.A natural avalanche cycle was reported north of Pemberton on Friday. Numerous natural avalanches size 3-4 were reported. An avalanche fatality occurred near Pemberton on Thursday, January 3. See the Preliminary Incident Report here. On Thursday, natural avalanches size 2-3 avalanches were reported north of Pemberton. Near the Coquihalla, wet avalanches size 2-2.5 were reported.

Snowpack Summary

50-100 cm of storm snow has accumulated throughout the region since January 1. Strong to extreme winds will have promoted slab formation and cornice growth. The recent storm snow sits on two weak layers that formed in mid and late December. These layers consists of surface hoar (feathery crystals) and/or a sun crust on steep south facing slopes. The surface hoar is reported to be most prominent in the southern part of the region in areas like the Coquihalla Summit and Manning Park, on north and east aspects at treeline.In the northern portion of the region, a deeper weak layer composed of facets (sugary snow) and/or surface hoar is buried 100 to 150 cm. There have been no reports of avalanche activity on this layer for the past week, but field observations suggest that avalanches may still be possible on this layer with a heavy load such as a cornice fall.

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.