Avalanche Forecast

Issued: Mar 12th, 2015 9:50AM

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

rbuhler, Avalanche Canada

Purcells.

"The green light is off." Unusually warm conditions with periods of strong sun and periods of rain have weakened the upper snowpack. Avoid sun-exposed slopes on Friday afternoon.Check out our blog on the current warm conditions: http://goo.gl/nS6uhF

Summary

Confidence

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

Weather Forecast

A ridge of high pressure should bring a mix of sun and cloud for Friday. Freezing levels are expected to reach around 2500m and alpine winds are forecast to be strong from SW by the end of the day. On Saturday, a weak storm system reaches the region. Models are currently showing 5-15mm between Saturday morning and Sunday morning. Freezing levels on Saturday are expected to stay around 2000m during the day but are forecast to fall to below 1000m by Sunday morning meaning rain may switch to snow at many elevations. During the storm, alpine winds are forecast to be strong from the SW. On Sunday, the storm should exit and a mix of sun and cloud can be expected with light winds.

Avalanche Summary

On Thursday, a natural cornice failure triggered a wind slab on the slope below. On Tuesday, loose wet avalanches and cornice failures from steep sun exposed slopes were reported. There have been some concerning avalanches in the neighboring Columbia regions including natural slabs releasing to ground and reactive wind slabs over facets being remotely triggered. On Friday, sunny and warm conditions are expected to destabilize the snowpack. Large avalanches have isolated potential to release on deep weak layers. Sluffing is expected from steep sun-exposed slopes and the triggering of wind slabs is possible in the alpine.

Snowpack Summary

A moist snow surface is being reported to around 2500m on solar aspects and 1800m on north aspects. Wind slabs are being reported 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

Wind slabs have developed on various aspects in the alpine. Warm temperatures and an underlying weak layer may increase the likelihood of triggering these wind slabs.

Use caution in lee areas in the alpine. Recent wind loading has created wind slabs.>Use ridges or ribs to avoid pockets of wind loaded snow.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Loose Wet

Warm temperatures and sun may result in loose wet avalanches releasing from steep terrain.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Sluffs may trigger deeper instabilities.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

Where enough snow overlies the mid-Feb crust/facet layer, reactive slab avalanches are possible. There is also a concern for avalanches to step-down to deeper weak layers due to the unseasonably warm temperatures.

Dig down to find and test weak layers before committing to a big line.>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 13th, 2015 2:00PM