Avalanche Forecast

Issued: Feb 8th, 2017 6:24PM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Storm Slabs and Persistent Slabs.

triley, Avalanche Canada

Purcells.

A Special Public Avalanche Warning Applies for this Region.Heavy loading from snow and wind is expected to result in natural avalanches, especially in the southern parts of the region.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

THURSDAY: Mainly cloudy with 15-25 cm of fresh snow, moderate to strong southwesterly winds, and freezing level remaining near valley bottoms.FRIDAY: Cloudy with scattered flurries bringing approximately 5 cm of fresh snow, moderate to strong southwesterly winds, and freezing level remaining at valley bottoms.SATURDAY: A mix of sun and cloud with isolated light flurries possible, moderate westerly winds, and freezing levels below valley bottoms.

Avalanche Summary

Reports from Tuesday include numerous explosives-triggered storm slab avalanches up to Size 2.5, with one Size 1 ski cut. Further evidence of numerous recent natural storm slab avalanches up to Size 2 was also reported. Also, a skier accidentally triggered a 50cm thick Size 2 storm slab avalanche on a southwest aspect at 2200 m.Heavy loading from snow and wind is expected to result in continued natural avalanche activity.

Snowpack Summary

Fresh snow totals from the past few days are around 50-100 cm in the southern part of the region, with the northernmost tip of the region only receiving about 25 cm of new snow. This recent storm snow has settled into a slab, especially where it has been wind-loaded, which is bonding poorly to the previous snow surface that includes sun crust on steep sun-exposed slopes, faceted snow, as well as surface hoar on sheltered open slopes. Weaknesses are also lingering within the recent storm snow, with 'upside-down' conditions and several easy to moderate shears being reported. A persistent weakness buried mid January is now down 60-120 cm and consists of buried surface hoar in sheltered areas, sun crust on south aspects, and/or faceted old snow. It has generally stabilized but may be sensitive to triggering in isolated areas where surface hoar is preserved. Another surface hoar/facet weakness buried mid-December found 70-140 cm is generally considered dormant. This and deeper persistent weaknesses remain concerns isolated to shallow snowpack areas where they lie closer to the surface.

Problems

Storm Slabs

Heavy loading from snow and wind is expected to result in natural storm slab avalanches. Be aware of the potential for storm slab avalanches to entrain loose snow or even 'step down' to a deeper weak layer.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.Be cautious as you transition into wind affected terrain.Watch for signs of instability such as whumpfing, or cracking.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

2 - 3

Persistent Slabs

Persistent slab problems may be back in play with the new load that has been added to the snowpack. Stick to supported terrain and exercise extra caution where the new snow has stacked onto a previously shallow snowpack.

Avoid convexities or areas with a thin or variable snowpack.Be aware of the potential for large avalanches due to the presence of deeply buried weak layers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Feb 9th, 2017 2:00PM