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Archived

Avalanche Forecast

Feb 24th, 2017–Feb 25th, 2017
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Purcells.

Choose supported terrain and watch for shallow snowpack areas where triggering a large persistent slab avalanche remains possible.

Confidence

High - The weather pattern is stable

Weather Forecast

SATURDAY: Flurries starting in the afternoon with trace accumulations, light west winds, alpine temperatures around -12 C.SUNDAY: Flurries with trace amounts in the north and up to 10 cm in the south, light winds, alpine temperatures around -12 C. MONDAY: Another 2-4 cm by the morning then clearing in the afternoon, light winds, alpine temperatures around -14 C.

Avalanche Summary

On Thursday, a natural size 2.5 persistent slab was reported on a south alpine aspect in the southern Purcells, failing on the February 3rd surface hoar 100 cm deep. A explosive cornice control mission on north aspects generally did not trigger slabs on the slopes below, with one exception of a slab in the recent storm snow. A few small loose dry avalanches were reported in steep terrain. Earlier in the week, there were several large skier triggered avalanches, 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 as well as sun crusts forming on steep 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. Storm snow from previous weeks is still bonding poorly to the February 3rd surface hoar / sun crust layer, which is now down 60-80 cm. A persistent weakness buried mid January is about a metre deep and the November crust is about 1.5 metres deep. These deep persistent weaknesses still have the potential to wake up and become reactive with human triggers. (See MIN post above).

Avalanche Problems

Persistent Slabs

A persistent weak layer of surface hoar and facets down 60-80 cm remains a concern in isolated areas. Smaller avalanches have the potential to step down to this and deeper persistent weaknesses, resulting in large avalanches.
Be aware of the potential for large avalanches due to the presence of deeply buried weak layers.Avoid steep convexities or areas with a thin or variable snowpack.Avoid lingering in runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3

Wind Slabs

Watch for wind slabs on lee and cross-loaded terrain.
Use caution above cliffs where small avalanches may have severe consequences.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: North, North East, East, South East, South.

Elevations: Alpine.

Likelihood: Possible

Expected Size: 1 - 2