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Avalanche Forecast

Archived

Mar 30th, 2021–Mar 31st, 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 unlikely, human triggered possible.
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 Coast.

The heat is on! 

Rising freezing levels and pockets of sunshine can pack a punch and quickly initiate natural avalanches. Back off slopes before the snow turns moist and avoid overhead hazards like cornices and large avalanche paths.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

A ridge of high pressure will keep the region mostly dry on Wednesday. A frontal wave will bring cloudy skies and light snow amounts by Thursday.

Wednesday: Mix of sun and cloud. Ridgetop wind moderate from the southwest. Alpine temperatures +6 degrees and freezing levels 2100 m.

Thursday: Cloudy with light precipitation. Ridgetop wind strong from the southwest. Alpine temperatures +5 and freezing levels 1900 m. 

Friday: Cloudy. Ridgetop wind light from the southwest. Alpine temperatures 1 and freezing levels 1000 m.

Avalanche Summary

Freezing levels are expected to rise to the mountain top on Wednesday. Warm temperatures and periods of sunshine will likely destabilize the snowpack and initiate natural avalanches. Pockets of wind slab may continue to be reactive to human triggering at upper elevations. 

Cornices are large and could also deteriorate under the warm spring sun. They require a large berth from above and below. 

On Sunday, a recent MIN report showed the new 10 cm of storm snow was easily running on a firm crust below 1200 m. 

Snowpack Summary

A mix of rain and snow brought 30-50 cm/mm of precipitation to the region since the weekend, accompanied by moderate to strong southerly winds. Strong and switching winds (SW to NW) may have formed fresh wind slabs below ridgelines. These wind slabs may be more reactive where they sit above a firm crust. The average snowpack depth at treeline elevations is 350 cm. 

A solid melt-freeze crust exists at lower elevations but will likely soften and destabilize during daytime warming.

Along ridgelines, cornices are large and may weaken when the sun comes out. 

Terrain and Travel

  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
  • Brief periods of sun could quickly initiate natural avalanche activity.
  • Be aware of highly variable recent wind loading patterns.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Cornices become weak with daytime heating or solar exposure.

Problems

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.

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.