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Avalanche Forecast

Archived

Apr 14th, 2021–Apr 15th, 2021

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

Regions

Northwest Inland.

Sustained warming continues to increase the likelihood for large cornice failures and wet loose avalanches. Start early and plan to be off large slopes before the heat of the day. 

Check out the latest Forecaster's Blog for more information on managing current conditions. 

Confidence

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

Weather Forecast

  

WEDNESDAY NIGHT: Clear / Light, southeast ridgetop wind / alpine low temperature 4 / Freezing level 2800 m.

THURSDAY: Sunny / Light, south ridgetop wind / alpine high temperature 9 / Freezing level 2900 m.

FRIDAY: Sunny / Light, southwest ridgetop wind / alpine high temperature 9 / Freezing level 3000 m.

SATURDAY: Sunny / Light, southwest ridgetop wind / alpine high temperature 8 / Freezing level 2900 m.

Avalanche Summary

Over the last few days there were many small (size 1) wet loose avalanches on south-facing slopes at all elevations and a few size 2-2.5 cornice failures on north and east facing slopes. 

The lower snowpack has been strong and settled over the past month, however, the dramatic warming this week could potentially wake up weak facets at the bottom of the snowpack. This is particularly a concern on steep, rocky slopes with a shallow or thin to thick snowpack. Cornice failures or a rider hitting a thin spot in the snowpack are the most likely ways to trigger these weak layers at the bottom of the snowpack.

Snowpack Summary

Sunny skies and rising freezing levels will result in melting surfaces everywhere except north-facing alpine terrain. In the alpine 5-20 cm. of snow is quickly settling and strengthening, although some wind slabs could linger on steep slopes. The recent snow has covered a variety of snow surfaces, including wind affected snow, crusts on solar aspects and at lower elevations, and soft snow on sheltered slopes at upper elevations.

The lower snowpack has been strong and settled over the past month, however the dramatic warming this week could potentially wake up weak facets at the bottom of the snowpack. This is particularly a concern on steep, rocky slopes with a shallow or thin to thick snowpack.

Cornices are large, looming, and capable of triggering large avalanches when they fail.

Terrain and Travel

  • Extra caution is needed around cornices under the current conditions.
  • Avoid exposure to slopes that have cornices overhead.
  • As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.