Avalanche Forecast

Issued: Apr 19th, 2015 8:11AM

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

triley, Avalanche Canada

Sea To Sky.

This is the last avalanche bulletin with danger ratings for this region this season.

Summary

Confidence

Poor - Due to the number of field observations

Weather Forecast

Mostly clear overnight with light winds and freezing levels remaining above 2400 metres. Mostly sunny with light winds and freezing levels rising up to about 3000 metres on Monday. Alpine temperatures are expected to be around +10 celcius. The ridge of high pressure is expected to break down sometime Tuesday allowing a weak system to move onto the south coast.

Avalanche Summary

On Saturday the overnight crust held up for most of the day resulting in only small loose wet avalanches and pin-wheeling. On Friday, numerous solar triggered natural loose wet avalanches up to size 2 were reported. One natural wet slab size 1.5 was reported that ran to the top of the run-out zone. A natural cornice failure size 1 also occurred and did not pull a slab from the slope below. With warming and periods of intense solar radiation avalanche danger will rise, solar triggered slab avalanches, failing cornices and loose wet avalanches will likely continue. Be aware of rapidly changing conditions.

Snowpack Summary

Upper elevations have received 25-40 cm of recent storm snow. The new snow sits on the April 10th persistent weak interface including crusts, facets and spotty surface hoar on high, northerly aspects. This interface has shown a poor bond and has been reactive naturally and to human triggers. Moderate to strong south west winds have redistributed the recent storm snow into wind slabs on leeward slopes and behind terrain features. The mid-March pwl is down 100-150 cm and has been producing hard, resistant results in snowpack tests and has been dormant. There is a low probability of triggering this layer, however; if it is triggered the consequence would be high. Large looming cornices may become weak with solar radiation and daytime warming. If a cornice fails it could trigger a large avalanche from the slope below.

Problems

Persistent Slabs

Two persistent weak layers sit in the upper snowpack. One is down 25-50 cm and has been recently reactive naturally, and to human triggers. The second one sits 100-150 cm down and may re-awaken with warming, cornice fall and step down avalanches.

Be aware of the potential for large, deep avalanches due to the presence of a buried crust/facet layer.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Cornices

Recent cornice growth has been observed, and large cornices are expected to become weak with solar radiation and daytime warming. Cornices falls could trigger large slab avalanches.

Pay attention to overhead hazards like cornices.>Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

3 - 5

Loose Wet

Solar radiation and rising freezing levels will deteriorate the snowpack quickly. Travel on sunny slopes early, and watch for signs of instabilities like avalanches, moist surface snow and snowballing.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 3

Valid until: Apr 20th, 2015 2:00PM