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Avalanche Forecast

Archived

Mar 12th, 2021–Mar 13th, 2021

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

Regions

South Columbia.

  Things are looking HOT up high for the next couple days. Overhead hazards such as cornice failures and wet loose avalanches on large alpine slopes will be the primary concern. Pay attention to what's above your head and back off of slopes if the snow surface becomes moist.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

  

FRIDAY NIGHT: Clear / Light, southwest ridgetop wind / alpine low temperature -11 / Freezing level valley bottom.

SATURDAY: Sunny / Light, southwest ridgetop wind / alpine high temperature 5 / Freezing level rapidly rising to 2500 m. and remaining elevated overnight.

SUNDAY: Sunny / Moderate, southwest ridgetop wind / alpine high temperature 5 / Freezing level 2300 m.

MONDAY: Mix of sun and cloud / Light, northeast ridgetop wind / alpine high temperature 2 / Freezing level 2000 m.

Avalanche Summary

On Thursday, there was report of a skier triggered size 2 storm slab avalanche on a southeast aspect in the alpine. The sun had warmed around 20 cm. of convective new snow just enough to react as a soft slab on a steep, convex feature.

The rapidly rising freezing level and sunny skies on Saturday are expected to elevate the avalanche hazard through the weekend.

Snowpack Summary

10-20 cm. of recent low density, convective snow is being warmed by sunny skies and forming soft slabs, especially in wind affected terrain in the alpine. The convective nature of spring storms results in widely varying snowfall amounts. Sunny skies are forming sun crusts on solar aspects which are breaking down during the heat of the day and increasing the likelihood for wet loose avalanches. Dry snow still exists on north aspects at upper elevations. Large cornices loom over alpine ridgetops.

Persistent weak layers of surface hoar, crusts, and/or facets 80-120 cm. down have recently been unreactive and no recent avalanches have been reported on these layers. However, big warm ups, like the one headed our way this weekend can awaken dormant weak layers resulting in large avalanches. Steep, rocky, convex terrain with a shallow or thin to thick snowpack are examples of places where triggering these layers are more likely.

Sunshine and warm temperatures often cause large cornice failures which are hazardous on their own and can also trigger large avalanches on deeper weak layers that the weight of a single rider would not trigger.

Terrain and Travel

  • Avoid exposure to slopes that have cornices overhead.
  • Cornice failure may trigger large avalanches.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.

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.

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.

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.