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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.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Minimize exposure to large looming cornices weakening with daytime warming and solar radiation and be cautious on sun-exposed slopes. 

Isolated pockets of wind slab may be found in immediate 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 to the Northern half of the region and light amounts to the South.

Tuesday: Mix of sun and cloud. Ridgetop wind light from the southwest. Alpine temperatures near -3 and freezing levels 2000 m. 

Wednesday: Snow 10-20 cm. Ridgetop wind moderate to strong from the southwest. Alpine temperatures -4 and freezing levels 1600 m. 

Thursday: Mix of sun and cloud with a trace of new snow. Ridgetop wind light from the southwest. Alpine temperatures near -6 and freezing lvels 1600 m. 

Avalanche Summary

On 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.  

A size 2 skier-triggered wind slab was reported in neighboring Glacier National Park on Saturday. A couple of size 2 cornice failures were reported on Friday, one triggering a thin wind slab on the slope below. 

A bit of cloud cover and a strong southwest wind is expected to keep snow surfaces cool on Tuesday. However; if the sun is shining in your local riding area, natural avalanche activity may spike.

Snowpack Summary

5-15 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 well to 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 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

  • 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.
  • Rocks will heat up with daytime warming and may become trigger points for loose wet avalanches

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.