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Avalanche Forecast

Archived

Jan 23rd, 2019–Jan 24th, 2019

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, human triggered possible.
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 possible, human triggered probable.

Regions

Purcells.

Choose conservative terrain and avoid being connected to large overhead slopes. Steep, rocky slopes with a variable thin to thick snowpack like ridgelines and open alpine bowls are more susceptible to human triggers.

Confidence

High -

Weather Forecast

Thursday: Mix of sun and cloud gusty westerly ridgetop winds. Alpine temperatures near -6 and freezing levels rising to 700 m.Friday: Mix of sun and cloud with moderate westerly ridgetop winds. Alpine temperatures high of -5 and freezing levels 1000 m. Saturday: Mix of sun and cloud with light to moderate westerly ridgetop winds. Alpine temperatures high of 0 degrees and freezing levels rising to 2500 m.

Avalanche Summary

No new avalanches reported on Tuesday. There is a MIN report that shows another deep persistent natural slab avalanche size 3.5 that happened last Saturday in International Basin. It may have been triggered by a wind event. Even though the weather pattern is fairly benign the deep persistent basal facet/ crust lingers just waiting for a weather event or a human trigger.Check out the MIN here.

Snowpack Summary

Up to 20 cm of recent snow has buried large surface hoar crystals and/or sun crusts. This will likely develop into a touchy problem in areas where a cohesive slab sits above the weak interface. The most suspect terrain features will be steep slopes and rolls between 1500 m- 2000 m (where the largest surface hoar exists) and steep south-facing slopes in the alpine (where sun crust exists). Reactive wind slabs can also be found at upper elevations on lee (N-NE) slopes. The weak nature of the snowpack lies at depth. The base of the snowpack is composed of weak faceted grains and a crust in many parts of the region. People have and will continue to be able to trigger these layers in areas where the snowpack is shallow. These areas typically include ridgelines, large open slopes and bowls at upper elevations. Common trigger points are rocks, trees and areas where the snowpack is variable (thin to thick and variable). If you trigger a deep persistent slab it will go big and be a destructive avalanche.

Problems

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.

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.