Avalanche Forecast

Issued: Apr 23rd, 2017 4:28PM

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

jsmith, Avalanche Canada

North Columbia.

The likelihood of cornices failing increases with intense sunshine and/or during the warmest parts of the day.

Summary

Confidence

Low - Due to the number of field observations

Weather Forecast

MONDAY: Mix of sun and cloud / Light southwest wind / Freezing level 1800mTUESDAY: Mostly cloudy with sunny periods / Light southwest wind / Freezing level 1900mWEDNESDAY: Mostly cloudy with isolated 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 natural cornice failure that triggered a size 3 persistent slab avalanche on a north aspect was reported on Saturday. 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. The entire seasons snowpack(roughly 300 cm) slid down to glacier ice in some areas. Exposure to large overhanging cornices remains a significant concern.

Snowpack Summary

Cornices continue to fall down and trigger large avalanches. Small wind slabs may still be lingering in isolated locations below alpine ridgetops. 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

Loose Wet

Small loose wet avalanches can still have big consequence if they push you into terrain traps such as cliffs and gullies.

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

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

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Apr 24th, 2017 2:00PM