Avalanche Forecast

Issued: Apr 16th, 2012 10:12AM

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

triley, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Due to limited field observations for the entire period

Weather Forecast

The wind is expected to build out of the west during the day on Monday and some light precipitation is forecast by Tuesday morning. Another weak ridge of high pressure is forecast to move into the interior ranges on Tuesday that should end the precipitation, but probably won't dry most areas up enough to see the sun. Gusty westerly winds are expected to develop overnight and rain showers and flurries should start by mid-day and continue into Wednesday night. Thursday is forecast to be unsettled with gusty southwest winds and periods of rain showers and flurries at higher elevations.

Avalanche Summary

Spring conditions exist in the region. Exposure to the sun, warm temperatures, and periods of rain are the most likely factors to influence the avalanche danger. If the temperatures go below freezing overnight, strong crusts should develop that are likely to hold the snowpack together. If the sun shines for a few hours, the crusts may break down quickly and moist surface snow avalanches may start running naturally. Continued warming from more sun, rain, or no overnight freeze, may cause surface avalanches to step down and trigger deeper wet slab avalanches. Prolonged warming may cause very deep releases on weak layers that were deposited early in the season, or on depth hoar that developed during the winter. It is important to monitor the temperature and the freezing levels as they may change rapidly from day to day.

Snowpack Summary

As we transition into spring the surface layers have a great deal of influence on the snowpack. When there is a solid re-frozen surface crust, travel is fast and easy, and the snowpack is held together by the surface cap. Any deeper persistent weak layers are unlikely to fail until the surface cap breaks down from daytime heating. When there is no crust, any deeper weak layers may fail depending on the amount of heat and the triggering force that is applied. If it cools off and snows, new snow and windslabs may not bond well to the hard spring crusts.

Problems

Loose Wet

Loose wet snow avalanches are expected during periods of daytime warming or if periods of rain showers persist. Loose snow avalanches may entrain a great deal of mass and may trigger deep weak layers.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 5

Wet Slabs

Wet slab avalanches may be triggered during periods of daytime warming or when there is no overnight freeze. Wide propagations are possible on the buried March crust.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 6

Deep Persistent Slabs

Avalanches may release on the deeply buried weak layers from February or from depth hoar that has developed during the winter. The likelihood will increase if warm temperatures persist and there is no overnight freeze.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 7

Valid until: Apr 17th, 2012 9:00AM