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Avalanche Forecast

Archived

Jan 12th, 2019–Jan 13th, 2019

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

Regions

Sea To Sky.

A major input of heat into the snowpack can wake up buried weak layers. A lot of uncertainty exists as to what will happen when temperatures climb. Uncertainty is best managed with conservative terrain.

Confidence

Low - Timing or intensity of solar radiation is uncertain

Weather Forecast

SATURDAY NIGHT: Cloudy with clear periods. Light southwest wind with moderate guests. temperature inversion with above freezing layer between 1500-2500 m.SUNDAY: Mainly cloudy. Light south wind with occasional moderate gusts. Alpine temps reaching +5 C, weak temperature inversion with above freezing layer between 1500-3000 m.MONDAY: Mix of sun and cloud. Light south-southeast wind. Alpine temps reaching +7 C, temperature inversion with above freezing layer between 1500-3000 m.TUESDAY: Sunny, Light south-southeast wind. Alpine temps reaching +6 C, freezing level dropping below 2000 m.More details can be found in the Mountain Weather Forecast.

Avalanche Summary

Friday morning explosives triggered large (size 2) cornice failures. As the snowpack warmed through the day, 30-50 cm surface snow gained reactivity as small slabs on convex and unsupported features. On Thursday morning, a natural storm slab avalanche cycle size 2-3 was reported on rocky features around 2000 m and loose wet avalanches were reported below 1700 m. Explosives triggered numerous size 1-2 storm slabs with good propagation across features. A MIN report from Thursday in Area 51 noted a rapid temperature rise and skiers triggered storm slab avalanches. See the MIN here.Numerous storm slab avalanches to size 2 were triggered by explosives and skiers on Wednesday. Additionally, a large (size 2) cornice failed under the weight of a person. On Monday, Several small wind slabs were triggered by skiers near ridge crest.

Snowpack Summary

Warm temperatures have moistened surface snow and promoted settlement. On Saturday morning, a melt-freeze crust was noted on all aspects up to 1900 m and south to southwest aspects in the alpine. Cold, dry snow may still be found on north aspects in the alpine. Cornices are large and suspect with warming. Warm temperatures are expected to penetrate to high alpine areas, poor overnight recoveries are expected up to 2000 m.The recent new snow has buried old wind slabs on a variety of slopes at alpine and treeline elevations. At treeline and below, two weak layers exist in the upper 2 m of the snowpack. These layers consist of surface hoar (feathery crystals) in more sheltered areas and a crust on solar aspects and on all aspects below 1600m.In the lower snowpack, a crust/facet (sugar snow) layer is now over 2 m deep. There have been no recent reports of avalanches on this layer, but it may still be reactive to heavy loads (such as a cornice fall) in isolated areas.

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.

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.