Avalanche Forecast

Issued: Apr 21st, 2017 4:50PM

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

jsmith, Avalanche Canada

North Columbia.

Cornice failures can trigger large avalanches on sugary facets near the bottom of the snowpack.

Summary

Confidence

Low - Due to the number of field observations

Weather Forecast

SATURDAY: Mostly cloudy with isolated flurries / Light to moderate southeast wind / Freezing level 2100mSUNDAY: Cloudy with flurries / Light to moderate southwest wind / Freezing level 1900mMONDAY: Cloudy with flurries / Light southwest wind / Freezing level 1800mNOTE: Convective flurries, which are common this time of year, can result in widely varying snowfall amounts. These spring squalls routinely drop 20+ cm of snow in one valley while the adjacent drainage remains dry. For this reason, the distribution of avalanche problems associated with new snow vary greatly within a region.

Avalanche Summary

A significant close call occurred near Mount Sir Sanford on Friday afternoon when a cornice failure triggered a size 3 persistent slab avalanche that involved multiple people. The avalanche occurred on a north aspect at approximately 2800m. Exposure to large overhanging cornices remains a significant concern.

Snowpack Summary

Recent new snow tree line and above has been redistributed by west and south winds. Cornices remain large and continue to become more overhanging. The middle of the snowpack is generally well settled and continues to transition into a spring melt/freeze regime except for high elevation northerly aspects. Expect the entire thickness of the snowpack to be moist or wet at lower elevations. At upper elevations a deep persistent layer consisting of facets sitting on a crust that was buried back in November has been sporadically reactive to heavy loads such as a cornice fall or the weight of a smaller avalanche running.

Problems

Cornices

Minimize exposure to slopes with large cornices overhead when it is cool and cloudy and completely avoid them if it is warm and/or sunny.

Cornice failures have the potential to trigger deeply buried weak layers.Cornices often break further back than expected; give them a wide berth when traveling on ridgetops.

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Wind Slabs

Lingering wind slabs may still be reactive in isolated areas below alpine ridgetops.

Pay attention to changing conditions with elevation.Be cautious with wind loaded pockets near ridge crests and roll-overs.Use ridges or ribs to avoid pockets of wind loaded snow.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2

Loose Wet

Loose wet avalanches may trigger deeply buried weak layers, resulting in large avalanches.

Pinwheeling snow below cliffs is a common sign that loose wet avalanches are becoming more likely.Solar radiation is a common trigger, especially where new snow is sitting on a crust.Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.

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

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Apr 22nd, 2017 2:00PM