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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

South 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. Ridgetop wind moderate from the West. Alpine temperatures near -9 and freezing levels 900 m.

Thursday: Mostly cloudy with some sunny periods and isolated flurries. Ridgetop wind light from the northwest. Alpine temperatures near -8 and freezing levels 1300 m.

Friday: Snow 10-15 cm. Ridgetop 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 1200 m.

Avalanche Summary

On Tuesday, a natural size 3.5 wet slab was reported from an S-SW aspect at 2500 m to 1800 m along with numerous wet loose avalanches up to size 1. A skier-triggered wind slab size 1 was mentioned from a North aspect at 2500 m and a skier-triggered cornice fall size 2.5 from an alpine ridgeline in Glacier National Park. 

New snow and strong winds shifting from the southwest to the 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 heavier snowfall amounts.

Snowpack Summary

New snow 5-15 cm fell 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 solar 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. 

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.