Avalanche Forecast

Archived

Feb 16th, 2021–Feb 17th, 2021

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.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

South Coast.

New snow has accumulated over a persistent weak layer and, at least initially, has not bonded well to the old surface. Give the snowpack time to heal, choose low angle terrain and avoid slopes that become sticky or moist.

Confidence

Low - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

TUESDAY NIGHT: Cloudy, clearing overnight / moderate northwest wind / ridgeline temperature low -5 / freezing level dropping below 500 m

WEDNESDAY: Mostly sunny with scattered clouds / light northerly wind / ridgeline temperature high +3 / freezing level around 1000 m

THURSDAY: Scattered clouds and incoming flurries beginning to accumulate overnight / moderate southerly wind / freezing level rising to about 1300 m in the afternoon

FRIDAY: Snow, up to 20-30 mm by morning / moderate southerly wind / ridgeline temperature high +1 / freezing level around 900 m

Avalanche Summary

Riders found soft low density storm snow rapidly gaining strength and reactivity as temperatures warmed Monday. Slab avalanches size 1-1.5 and 15-30 cm deep released naturally and were triggered by skiers and explosives in the afternoon. There are some tremendous visuals in this MIN report.

Snowpack Summary

Warm temperatures have transitions 15-30 cm new snow from low density powder to moist snow and crusts. At upper and alpine elevations, dry snow sits on a variety of wind affected surfaces and older crusts.

Click here to check out North Shore Rescue's snowpack update from February 12. It's an excellent snapshot of conditions on the North Shore prior to the advance of the recent storm pattern.

Beneath 15-30 cm recent snow there is a rather unusual mix of facets, thin breakable crust and isolated pockets of surface hoar. There is then 30-40 cm of gradually faceting snow, and then a wide spread and supportive crust underneath.

Terrain and Travel

Closely monitor how the new snow is bonding to the old surface.
Be alert to conditions that change with elevation.
Watch for unstable snow on specific terrain features, especially when the snow is moist or wet.
Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet

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.