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Avalanche Forecast

Archived

Feb 25th, 2017–Feb 26th, 2017

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

Purcells.

Light flurries the next few days with greater accumulations in the south part of the region. Watch for shallow snowpack areas where triggering persistent slab avalanches remains possible.

Confidence

High - The weather pattern is stable

Weather Forecast

SUNDAY: Flurries with 4-8 cm of new snow and possibly greater accumulations in the south part of the region, light variable winds, alpine temperatures around -15 C.MONDAY: Continued light flurries with another 3-5 cm of new snow, light southwest winds, alpine temperatures around -15 C.TUESDAY: Mix of sun and cloud, light west winds with moderate gusts, alpine temperatures around -15 C.

Avalanche Summary

On Friday, several skier triggered size 1-1.5 slabs were reported on steep convex alpine features (30 cm deep). Several large natural persistent slab avalanches have been reported on the western slopes of the Purcells, including a cornice triggered size 3.5 avalanche on the November crust and two size 2.5 avalanches the February 3rd surface hoar. Several large skier triggered avalanches were reported last week, including a remotely triggered size 2 wind slab near Kimberly, a skier-triggered size 2.5 persistent slab near Golden, and a remotely-triggered size 3 persistent slab near Golden. See here for a MIN report from one of the large avalanches near Golden.

Snowpack Summary

Light flurries over the past few days delivered 10-25 cm of low density snow. Expect to find isolated pockets with thicker wind deposits at higher elevations and sun crusts forming on south-facing slopes. The recent snow has buried the mid-February interface, which is composed of a thick rain crust up to about 2000 m, sun crusts on steep solar aspects, and spotty surface hoar on shaded aspects. Several deeper weak layers remain a concern including the February 3rd interface (50-80 cm deep) in the southern Purcells and the mid-January interface in the northern Purcells (about 100 cm deep). Basal facets may still be a reactive in shallow rocky start zones.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.