Avalanche Forecast

Issued: Apr 22nd, 2017 4:13PM

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

jsmith, Avalanche Canada

Purcells.

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.

Summary

Confidence

Low - Due to the number of field observations

Weather Forecast

SUNDAY: Mix of sun and cloud with isolated flurries / Light southwest wind / Freezing level 2100mMONDAY: Cloudy with isolated flurries / Light southwest wind / Freezing level 2000mTUESDAY: Mix of sun and cloud with isolated flurries / Light to moderate southwest wind / Freezing level 1900mNOTE: 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

Two large cornice failures were reported on north aspects in this region on Friday. One did not trigger a slab and the other triggered a small slab which entrained loose snow and ran for approximately 800 m. 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 failure 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.

Cornices often break further back than expected; give them a wide berth when traveling on ridgetops.Cornice failures could trigger large avalanches on sugary facets near the bottom of the snowpack.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 4

Loose Wet

Convective flurries and warm temperatures could produce loose wet avalanches in the afternoon.

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.Pinwheeling snow below cliffs is a common sign that loose wet avalanches are becoming more likely.

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

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Wind Slabs

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

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

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Apr 23rd, 2017 2:00PM