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Avalanche Forecast

Archived

Jan 17th, 2019–Jan 18th, 2019

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

Regions

South Rockies.

Modest snowfall is gradually burying a new weak layer, while triggering large avalanches is still possible in steep rocky terrain.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

THURSDAY NIGHT: Light flurries with localized accumulations of 5-10 cm, moderate west wind increasing in speed overnight, alpine temperatures drop to -16 C.FRIDAY: Mostly cloudy with isolated flurries, strong west wind, alpine high temperatures around -6 C.SATURDAY: 5-15 cm of snow, strong southwest wind, freezing level climbing to 1500 m, alpine high temperatures around -4 C.SUNDAY: Mostly cloudy then clearing in the afternoon, strong west wind, alpine high temperatures around -6 C.

Avalanche Summary

By Thursday afternoon, skier traffic produced a few small (size 1) avalanches in the new snow.The most recent reports of larger avalanches are from last weekend when warm temperatures stressed some of the deeper layers in the snowpack. On Saturday, a size 2 natural deep persistent slab avalanche was observed on a south facing slope at 2100 m (more details here). There is also a great MIN report from the neighboring Lizard Range where a group of sledders share about their near miss on a steep southwest facing feature at ridgecrest.

Snowpack Summary

The new snow is burying large surface hoar crystals and/or sun crusts, which could eventually develop into a touchy problem as snow accumulates. The most suspect terrain features will be steep slopes and rolls below 2000 m (where the largest surface hoar exists) and steep south-facing slopes in the alpine (where sun crusts exist).Large variability in snow depths still exists in the region, ranging from almost no snow to nearly 200 cm in some areas. For average snowpack areas, expect to find weak and sugary faceted snow around 50 to 100 cm deep, which extend to the ground. This weak bottom half of the snowpack has been the culprit for large avalanches in the region over the past few weeks.

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.

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.