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Avalanche Forecast

Archived

Apr 5th, 2021–Apr 6th, 2021

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

Periods of sunshine can pack a punch and trigger natural avalanches and cornice fall. Give cornices a wide berth from above and below. 

Pockets of wind slab may exist and be reactive to human triggering on leeward features in the alpine.

Confidence

High -

Weather Forecast

The region will start to see the effects of the next frontal system by Tuesday night. This will bring moderate snow amounts accompanied by strong southwest wind.

Tuesday: Mix of sun and cloud. Ridgetop wind strong from the southwest. Alpine temperatures near -3 and freezing levels 1600 m. 

Wednesday: Snow 10-20 cm. Ridgetop wind moderate to strong from the southwest. Alpine temperatures -3 and freezing levels 1400 m. 

Thursday: Mix of sun and cloud with a trace of new snow. Ridgetop wind light from the southwest. Alpine temperatures near -4 and freezing lvels 1400 m. 

Avalanche Summary

On Monday a size 3 natural wind slab was reported on a North aspect at 2400 m. 

Large (size 2-3) natural cornice failures have been reported recently, one on Sunday triggered a 30 cm deep storm slab. 

A bit of cloud cover and a strong southwest wind is expected to keep snow surfaces cool on Tuesday. Natural avalanche activity may taper. However; things can change rapidly when the sun shines. Natural avalanche activity and cornice failures could then spike.

Snowpack Summary

10-30 cm of recent snow accompanied by strong southwest wind may have formed wind slabs on leeward slopes at upper elevations. Reports indicate the snow is bonding to the underlying surfaces which include wind-affected snow in the alpine or crust on solar aspects and below 1900 m. Below this elevation and on solar aspects the new snow dusts crusty surfaces down to 1500 m. Below 1500 m, the moist snowpack is quickly diminishing.

At alpine and treeline elevations, a widespread crust exists (except on north-facing slopes above 1800 m) buried 50-100 cm deep. Overall the snow seems to be bonding well at this interface, although there have been a few isolated avalanches running on deeper crust layers over the past few weeks.

Terrain and Travel

  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Use ridges or ribs to avoid areas of wind loaded snow.
  • Be alert to conditions that change with elevation and sun exposure.

Problems

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.

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.