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Avalanche Forecast

Archived

Apr 7th, 2021–Apr 8th, 2021

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

Regions

Sea To Sky.

Fresh snow amounts are variable across the region, and may have formed reactive wind slabs on many aspects due to changing wind directions. 

Keep in mind that even brief periods of sun could initiate avalanche activity in the new snow.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Wednesday night - Snow, 5-10 cm / moderate west wind / alpine low temperature near -9 / freezing level at or near valley bottom

Thursday - A mix of sun and cloud / light to moderate northwest wind / alpine high temperature near -8 / freezing level 1100 m

Friday - Snow, 10-15 cm / strong southwest wind / alpine high temperature near -7 / freezing level 900 m 

Saturday - Mainly sunny / light to moderate northwest wind / alpine high temperature near -7 / freezing level 1200 m

Avalanche Summary

Reactive wind slabs may be found on a variety of aspects due to changing wind directions.

A natural avalanche cycle was observed in the region on Saturday during the storm. On Sunday, there were a few size 1-1.5 human triggered wind slab avalanches reported. This MIN describes triggering a small wind slab in large terrain. There were a few small dry loose avalanches reported on Tuesday.

Snowpack Summary

5-10 cm of snow accumulated throughout the day on Wednesday, and another 5-10 is expected to fall on Wednesday night. This adds to the 20 cm that fell over the weekend. The recent precipitation likely fell as rain below around 1000 m. Moderate to strong winds have likely formed wind slabs in lee terrain features.

The new snow sits on a crust on sun-exposed aspects, and on all aspects below 1600 m, and on soft snow or wind slabs on north aspects. 

Cornices are large and looming along ridgelines. Their release is unpredictable, requiring a large berth if you're travelling above or below them.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of highly variable recent wind loading patterns.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.