Avalanche Forecast

Issued: Jan 30th, 2012 9:26AM

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

swerner, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Freezing levels are uncertain on Wednesday

Weather Forecast

Tuesday: Trace of new snow. Ridgetop winds 20-55km/hr from the West. Freezing levels may rise to 800m. Treeline temperatures near -5. Wednesday: Snow amounts near 5cms. Ridgetop winds 30-40km/hr from the NW. Freezing levels near 800m dropping to valley bottom. Thursday: A ridge will bring warmer air, elevating freezing levels up to 1500m. The region looks to remain dry well into Saturday.

Avalanche Summary

Current observations include one large size 3.5 slab avalanche that occurred west of Invermere at 2300m on a SE-SW aspect, 600m wide, running 1300m in length, and the slab pulled out to the ground basal layers. A few smaller (size 2) avalanches were reported on NE-E aspects above 2300m on an old failure plane within the snowpack. Older, yet a reminder is the control work in the Dogtooths that produced avalanches running to ground on basal facets & depth hoar in high elevation terrain with light loads on Jan. 27th. Further south that day, large loads produced very little results at mid elevations with large loads.

Snowpack Summary

The Purcell's are one of the more complex & variable snow packs in the province right now.The storm over the weekend delivered 20 - 40 cm of snow to the region with moderate gusting strong winds out of the SW, S & a bit of SE. This snow fell on a snow pack that is for the most part, pretty well settled.There are a few exceptions though:The Jan. 13th SH/FC combo is still reactive in ski hill testing, but this needs to be taken with a grain of salt as this snowpack is a bit artificial when compared to a true backcountry uncontrolled snowpack. Regardless, I feel like we can't take our eyes off this layer just yet, remember, it's only two weeks old.It sounds like there is a lot of strong snow over the mid December facet layer which is buried approx. 80 cm on the east side and 200+ cm on the west side. This layer seems to have more energy in the Purcells than any other region in the province. On Jan. 28th a skier remotely triggered a size 3 avalanche & this layer was suspected as the weakness.There are basal facets at the ground which are a concern, especially on shady high elevation slopes. Snowpack depths at 2000m sit near 2m deep.

Problems

Wind Slabs

New snow and winds blowing from all directions have formed wind slabs on most slopes. You're likely to find the bigger wind slabs on N, NE, & E facing aspects but you need to be suspect of all open slopes at and above treeline. Wind slab are touchy.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 5

Storm Slabs

New snow over the weekend developed storm slab instabilities. It may take a few days for the storm snow to settle out. You should remain diligent in both travel techniques and terrain choices. Staying conservative is appropriate.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

Recent avalanche activity indicates that deeply buried weak layers are once again reactive to light loads. A skier, sledder or avalanche running in the storm snow could trigger a large avalanche, especially in steep rocky terrain.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

4 - 7

Valid until: Jan 31st, 2012 8:00AM