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Avalanche Forecast

Archived

Jan 15th, 2019–Jan 16th, 2019

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

Regions

Sea To Sky.

Be aware of places with a thin, shallow snowpack or areas which hold pockets of cold, dry snow. These are most suspect for lingering problems.

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Thursday

Weather Forecast

TUESDAY NIGHT: Cloudy with clear periods. Freezing level dropping to valley bottom. Alpine temperatures around 0. Light southeast winds. WEDNESDAY: Mix of sun and cloud. Freezing level below 1600 m. Alpine high near 0. Light east-southeast winds. THURSDAY: Cloudy with isolated flurries, up to 5 cm. Freezing level at valley bottom, chance of inversion. Alpine high near -1. Light to moderate east-southeast winds.FRIDAY: Isolated flurries, up to 10 cm and snowfall continuing into Saturday. Freezing level 1400 m. Alpine high -1. Moderate south-southeast wind.More details can be found in the Mountain Weather Forecast.

Avalanche Summary

Explosives triggered small cornices and one size 2 loose-wet avalanche in the alpine around mid-day Monday. On Sunday, two very large (size 3) slab avalanches were reported in the region. These avalanches occurred around 1500-1900 m and were observed on south-south east aspects. It is likely that that solar warming and sloughing triggered these avalanches Friday or Saturday. On Saturday, several large cornice falls were triggered naturally and with explosives. Some of these triggered size 2 slabs on slopes below. There is a trend of cornice falls increasing in size and frequency as the warm weather continues. Loose wet avalanches to size 2 were also failing naturally on sunny aspects on Saturday with continued reports into Sunday.

Snowpack Summary

Warm temperatures can weaken surface snow layers and have recently made cornices touchy. The warmth can also penetrate into more deeply buried weak layers. Colder overnight temperatures are promoting better recovery of the snowpack, making for easier travel in the morning. Refrozen crusts may be found on all aspects below about 1800-2000 m; and on sunny aspects in the alpine. These may break down with warming through the day. Cold, dry and wind-affected snow may still be found on more north-facing and polar aspects in the alpine. Variable instabilities exist in recent storm snow layers. Two weak layers exist in the upper 2 m of the snowpack at and below treeline. 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. This layer may still be reactive to heavy loads (such as a cornice fall) in isolated areas.

Problems

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.

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.