Avalanche Forecast

Issued: Apr 18th, 2015 8:38AM

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.

Strong solar radiation, high freezing levels, and very warm temperatures may increase the avalanche danger rapidly. If there is no overnight re-freeze in your area, you should avoid avalanche terrain.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

Mostly clear with light northwest winds overnight, and freezing levels dropping down to about 2000 metres. Sunny and warm on Sunday with a chance of some thin high cloud. Freezing level rising up to 2800 metres with temperatures around +10 expected in the alpine. Sunny and warm on Monday with freezing levels around 2800 metres. The ridge of high pressure is forecast to break down late Monday or early Tuesday allowing a weak westerly flow to move onshore bringing cloud and light precipitation.

Avalanche Summary

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.

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

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.

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

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 3

Valid until: Apr 19th, 2015 2:00PM