Avalanche Forecast

Issued: Mar 13th, 2015 10:02AM

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

rbuhler, Avalanche Canada

Purcells.

Storm conditions will quickly elevate the hazard on Saturday. We are uncertain how the snowpack will react to this new loading and are recommending very conservative terrain choices if you head out during the storm.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

A warm storm hits the region on Saturday. Models are currently showing 15-30mm of precipitation but freezing levels are forecast to stay around 2000m during the day so much of it will fall as rain. Freezing levels are forecast to drop down to below 1000m by Sunday morning so the rain may switch to snow at the end of the storm. Alpine winds are forecast to be strong during the storm and ease by Sunday morning. On Sunday, a mix of sun and cloud is expected with freezing levels around 1000-1500m and light alpine winds. There is currently uncertainty regarding Sunday night and Monday. A second storm pulse may affect the region but it also has the potential to track too far to the south and completely miss the region.

Avalanche Summary

On Thursday, a cornice failure triggered a small wind slab on the slope below and a natural size 2 slab was reported from a steep rocky sun-exposed slope.Â There have been some concerning avalanches in the neighboring Columbia regions over the last few days including natural slabs releasing to ground and very reactive wind slabs over facets being remotely triggered. Saturday's storm is expected to quickly build touchy new wind slabs where the precipitation falls as snow.Â At lower elevations where the precipitation falls as rain, loose wet avalanches can be expected.Â The major question and my biggest concern is whether deeply buried persistent weaknesses will wake-up with the new loading. Â These persistent weak layers could have the potential to result in some very large persistent slab avalanches.Â However, this is probably a low probability, high consequence type of problem.

Snowpack Summary

A moist snow surface has been reported to around 2500m on solar aspects and 1800m on north aspects. Wind slabs have formed in the alpine and may be overlying the early-March crust/facet layer. The late-Jan crust/surface hoar layer can be found about a metre below the surface in deeper snowpack areas. The mid-January surface hoar can be found below that. These layers have gained significant strength and have been dormant for several weeks but have the potential to wake-up with the current warm temperatures.

Problems

Wind Slabs

At higher elevations, new snow and strong winds will quickly build wind slabs. Warm temperatures and an underlying weak layer may increase the likelihood of triggering these wind slabs.

Use ridges or ribs to avoid pockets of wind loaded snow.>Avoid freshly wind loaded features.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 3

Loose Wet

Rain on Saturday may result in loose wet avalanches releasing from steep terrain.

Avoid avalanche terrain during periods of rain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

New loading from rain or snow coupled with the persistent warm conditions may overload buried persistent weak layers resulting in very large avalanches.

Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.>Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Mar 14th, 2015 2:00PM