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Avalanche Forecast

Archived

Apr 6th, 2021–Apr 7th, 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.

Wintery weather returns with new snow and strong wind on Wednesday. Fresh wind slabs may be reactive on lee slopes at upper elevations.

Loose-dry avalanches will likely occur from steep slopes and terrain features. 

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Tuesday Night: Cloud cover starts to develop. Ridgetop wind moderate from the southwest and freezing levels 1200 m. 

Wednesday: Snow amounts 10-20 cm. Ridgetop wind strong from the southwest. Alpine temperatures near -5 and freezing levels 1500 m. 

Thursday: Mostly cloudy with light snow 5-10 cm. Ridgetop wind light from the southwest. Alpine temperatures near -5 and freezing levels 1200 m.

Friday: Snow 5-10 cm. Ridgetop wind moderate to strong from the South. Alpine temperatures near -8 and freezing levels 1200 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 avalanches up to size 1.5.

On Monday a size 3 natural wind slab was reported on a North aspect at 2400 m. Additional reports of natural loose wet avalanches up to size 1 were seen from most solar slopes in the alpine and cornice fall size 2-2.5 on a northeast aspect.

With forecast snow and strong southwest wind on Wednesday, wind slabs may be reactive on leeward slopes, and natural loose-dry sluffing seen from steep terrain 

Snowpack Summary

Winter weather returns with light to moderate forecast snow amounts accompanied by moderate wind through the forecast period. Fresh wind slabs may build through the day on Wednesday. The new snow sits above surface hoar crystals on sheltered north facing terrain above 1900 m, a series of melt-freeze crusts on all aspects below 1900 m, and a sun crust on the southerly aspects to mountain top. Below 1500 m the snowpack is quickly diminishing.

Loose–dry sluffing will likely occur on steep slopes and terrain features where the new snow has a poor bond to the underlying old surfaces. 

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

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.

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.