Avalanche Forecast

Issued: Mar 14th, 2015 9:49AM

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.

Stormy conditions continue on Sunday in the south of the region. Tricky conditions are expected in the alpine and conservative decision making is essential.

Summary

Confidence

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

Weather Forecast

Variable conditions are expected for Sunday across the region. A ridge of high pressure building over central BC should keep the north of the region mainly dry. A storm system will track south of the US border on Sunday and should bring light to moderate precipitation to the southern half of the region. Freezing levels on Sunday are expected be around 1500m and alpine winds should be moderate from variable directions. On Monday, the north of the region should stay mainly dry but the south of the region may see lingering precipitation. WInds should be light and freezing levels around 1500m. Tuesday looks to be unsettled and freezing levels may reach over 2000m.

Avalanche Summary

On Friday, numerous loose wet avalanches up to size 2 were reported from solar aspect slopes. 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. During the last few days there have been some concerning avalanches in the neighboring Columbia regions including natural slabs releasing to ground and very reactive wind slabs over facets being remotely triggered. On Sunday, touchy wind slabs are expected in the alpine and loose wet sluffing is possible from steep slopes at lower elevations. There is a still a concern for avalanches to step down to deeply buried weak layers resulting in larger persistent slab avalanches.

Snowpack Summary

At higher elevations, new snow sits over a variety of surfaces including moist snow, crusts, wind affected surfaces, and/or old wind slabs which may still be reactive. Rain has soaked the upper snowpack to around treeline elevation. In the alpine, strong winds during the storm are redistributing the new snow into wind slabs in leeward terrain features. Prior to the storm, 10-30cm of snow was sitting over a weak facet/crust layer that was buried in mid-February. The late-Jan crust/surface hoar layer can be found around 1m 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 and loading.

Problems

Wind Slabs

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

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

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 3

Loose Wet

Ongoing rain at lower elevations 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

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Mar 15th, 2015 2:00PM