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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

North Columbia.

 

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: Cloudy with snow up 5-10 cm. Ridgteop wind moderate from the northwest. Alpine temperatures near -6 and freezing levels valley bottom.

Thursday: Mostly cloudy with some sunny periods and isolated flurries. Ridgetop wind light from the northwest. Alpine temperatures near -5 and freezing levels 1300 m.

Friday: Snow 10-15 cm. Ridgteop wind strong from the southwest. Alpine temperatures near -8 and freezing levels 900 m.

Saturday: Snow 5-10 cm. Light to moderate West wind and freezing levels 1300 m.

Avalanche Summary

On Tuesday, a skier-triggered cornice failure size 2.5 was reported from a high alpine ridgeline along with some wet loose and wet slab avalanches up to size 2.

New snow and strong winds shifting from the southwest to northwest may have formed fresh and reactive wind slabs on leeward slopes at treeline and in the alpine. 

Loose surface avalanches within the new snow may occur from steeper slopes and terrain features, especially if the sun comes out, and in locations that received greater accumulations of new snow.

Snowpack Summary

Winter weather returns with new snow 10-20 cm across the region. Shifting wind directions from the southwest to northwest could form new wind slabs on leeward slopes and behind terrain features. The new snow sits on a series of melt-freeze crusts on all aspects below 1900 m and southerly aspects to mountain top. On North aspects in the alpine, the new snow will sit on dry wintery snow surfaces and possibly surface hoar on wind-sheltered slopes. 

The recent warm weather is expected to have helped old persistent weak layers heal, including a few crusts buried over the last month as well as a facet layer 150 cm deep from the mid-February cold snap.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Use ridges or ribs to avoid areas of wind loaded snow.
  • Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.
  • 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.