Avalanche Forecast

Issued: Apr 18th, 2012 4:00PM

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

triley, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Due to limited field observations for the entire period

Weather Forecast

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. The freezing level is forecast to rise to about 2000 metres by Thursday evening. The next Pacific frontal system is forecast to move into the interior by early Friday morning. Expect 5-10 mm of precipitation combined with freezing levels down to about 1600 metres. A weak ridge is forecast to build from south of the border on Saturday that should dry out the interior regions.

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 avalanches are expected during periods of daytime warming and during periods of rain showers. Overnight freezing above about 1500 metres should develop a hard crust that may deteriorate during the heat of the day.

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 5

Wet Slabs

Wet slab avalanches are expected during periods of daytime warming and during periods of rain showers. Overnight freezing above about 1500 metres should develop a hard crust that may deteriorate during the heat of the day.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 7

Wind Slabs

New snow may be transported into wind slabs that are easy to trigger on northerly aspects in the alpine.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Apr 19th, 2012 9:00AM