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Avalanche Forecast

Archived

Jan 11th, 2019–Jan 13th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Vancouver Island.

 

Confidence

Moderate - Fluctuating freezing levels, no observations from public.

Travel & Terrain Advice

Be aware of changes in conditions with elevation. Small loose wet avalanches can have large consequences when combined with terrain traps. Rocks and trees releasing snow is an indication of instability. Avoid wind loaded features and convex rolls in the alpine. Give cornices a wide berth above and below.

Avalanche Summary

Avalanche control on Mount Washington Wednesday produced numerous size 1-2 storm slab avalanches triggered both with explosives and ski cuts. These slabs were at treeline on all aspects and were between 20 and 80 cm deep. Avalanches were touchy and propagated far and into low angled and treed terrain. The failure layer in these avalanches was loose dry storm snow that was subsequently loaded with 40-60 cm of dense new snow and some buried surface hoar in protected terrain. Thursday saw widespread small natural loose wet avalanches on all aspects below 1600 m.

Snowpack Summary

Over 100 cm of new snow has fallen at treeline since Tuesday. This new snow overlies a variety of old surfaces including buried surface hoar, old exposed crusts and loose dry storm snow. During the height of the precipitation, temperatures and freezing levels rose and strong SE winds were associated. This created deep pockets of reactive cohesive storm slabs ranging in depth from 20-80+ cm deep. All aspects below 1600 m were then saturated with 20-30 mm of rain on Thursday with extensive tree bombing and natural loose wet activity from steep rocky terrain. Layers below this recent load have shown no signs of reactivity and appear to be settling and bonding well.

Snowpack Summary

Surface: Saturated new snow below 1600 m, wind affected and deep pockets above 1800 m. Upper: 50-100 cm of storm snow, rain soaked at treeline and below, drier in the alpine. Mid: Well settled with several unreactive crusts. Lower: well settled.

Past Weather

Vigorous storm on Wednesday depositing 70+ cm of dense new snow at treeline with moderate to strong SE winds followed by warming temperatures, rising freezing levels and 20-30 mm of rain on Thursday.

Weather Forecast

FRIDAY: 10-25 mm of precipitation with freezing levels around 1700 m. Winds extreme above treeline easing to strong from the SE.

SATURDAY: 5-10 mm of precipitation with freezing levels spiking up to 2200 m. Winds strong from the SE.

SUNDAY: Trace amounts of precipitation with freezing levels around 1600 m. Winds light from the SE veering W to NW in the afternoon.

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.

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.

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.