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Avalanche Forecast

Archived

Mar 16th, 2021–Mar 17th, 2021

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

Sea To Sky.

It is possible that riders could trigger wind slabs in steep terrain. Look for signs of instability in your riding area, such as recent avalanche activity.

Confidence

High -

Weather Forecast

TUESDAY NIGHT: Partly cloudy, 10 to 20 km/h southwest wind, alpine temperature -5 C.

WEDNESDAY: Increasing cloud with afternoon flurries, accumulation 1 to 3 cm, 20 to 30 km/h south wind, alpine temperature -4 C, freezing level 1500 m.

THURSDAY: Cloudy with snowfall, accumulation 5 to 10 cm, 40 to 60 km/h southeast wind, alpine temperature -3 C.

FRIDAY: Cloudy with snowfall, accumulation 20 to 40 cm, 40 to 60 km/h south wind, alpine temperature -6 C.

Avalanche Summary

Cornices were triggered by explosives on Monday and Tuesday, releasing large chunks that could kill a person. Small to large (size 1 to 2.5) slabs were triggered by skiers, explosives, and naturally on Monday within the recent 10 to 20 cm of storm snow. 

There's evidence of some large avalanches in the past week around the Whistler area, including near Mt. Fee (see here and here) and last week on Mt. Fissile in the Whistler backcountry. These avalanches may be due to extensive wind loading, but they may also be associated with isolated weak snow from earlier this season.

Snowpack Summary

Wind slabs may linger in steep, lee terrain features at treeline and alpine elevations from Sunday's 15 to 20 cm of snow with extreme southeast wind. The wind slabs could be substantially thicker immediately adjacent to ridges from rapid snow loading during the storm. Expect to find a hard melt-freeze crust on sun-exposed slopes and on all aspects below around 1500 m. The crust may weaken into moist snow on sun-exposed slopes if sunny skies prevail. Along ridgelines, cornices are large and will weaken with daytime warming.

Around 100 to 300 cm of consolidated snow may overly sugary faceted grains formed earlier this season. These layers are expected to be spotty around the region and we haven't received conclusive evidence of them being the culprit of avalanche activity. That being said, it is possible they may be associated with a few recent large avalanches around the Whistler area.

Terrain and Travel

  • Carefully evaluate steep lines for wind slabs.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Extra caution is needed around cornices under the current conditions.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.