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Avalanche Forecast

Archived

Apr 6th, 2021–Apr 7th, 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.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Wintery weather returns with new snow and strong wind on Wednesday. Fresh pockets of wind slab may be reactive on lee slopes in the alpine.

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

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

The higher snow amounts will likely exist in the Northern parts of the region.

Tuesday Night: Clear. Ridgetop wind light to moderate from the South and freezing levels 1200 m. 

Wednesday: Snow amounts 5-15 cm. Ridgetop wind moderate from the southwest. Alpine temperatures near -1 and freezing levels 1600 m. 

Thursday: Mix of sun and cloud with scattered flurries up to 5 cm. Ridgetop wind light from the southwest. Alpine temperatures near -1 and freezing levels 1400 m.

Friday: Snow 5-10 cm. Ridgetop wind moderate to strong from the South. Alpine temperatures near -5 and freezing levels 1400 m.

Avalanche Summary

On Monday, skier-controlled and natural size 1 slabs were failing within the recent storm snow on solar slopes. The terrain features were steep convex rolls.

Sunday several loose-dry and skier-triggered size 1.5 avalanches were reported. The reactivity mostly occurred during daytime warming from steep slopes within the new snow.  

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

Snowpack Summary

Winter weather returns with light 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 a melt-freeze crust exists and 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 few layers of note are buried 50-100 cm deep including a layer of small surface hoar crystals on shady, wind-sheltered aspects and a series of crusts on solar aspects and below 1800 m. Overall the snow seems to be bonding well to these interfaces, although there have been a few isolated avalanches running on deeper crust layers in the past week.

Terrain and Travel

  • Watch for wind-loaded pockets especially around ridgecrest and in extreme 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.