Avalanche Forecast

Issued: Apr 2nd, 2013 10:04AM

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

mbender, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain for the entire period

Weather Forecast

Wednesday: Overcast skies / Light northwest winds / Freezing level at 1700mThursday: A high pressure system builds promoting clear and dry conditions with light westerly winds and 1800m freezing levels.Friday: An upper trough of low pressure will move over the Interior on Friday bringing light to locally moderate precipitation. Freezing levels will be in the valley bottom in the morning and rise to 1700m in the afternoon.

Avalanche Summary

Numerous natural loose wet and wet slab avalanches up to size 2.5 have recently been reported from solar aspects at a treeline and above.

Snowpack Summary

Surface faceting and surface hoar growth (up to 20 mm) has been prevalent on high, shady aspects, while the surface snow on sun-exposed slopes and at lower elevations (below 2000m) has been subject to daily melt-freeze cycles.Cornices are large and weak. Pockets of wind slab can be found on lee slopes and are possible to trigger under your skis or sled.A layer of buried surface hoar sitting on a crust down around 70-120cm, and has been producing variable results in snowpack tests. This persistent weakness remains a concern because of the potential for very large avalanches particularly with heavy triggers such as cornice falls. Old deep persistent weaknesses, including basal depth hoar, are a concern in shallow snowpack areas.

Problems

Cornices

Natural cornice falls are a concern during daytime warming. Cornices may also be triggered easily by traveling near them.

Cornices become weak with daytime heating, so travel early on exposed slopes.>Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 5

Loose Wet

Expect to see wet loose snow avalanches out of steep rocky sun-exposed slopes. Natural avalanche activity. snowballing, moist and wet snow surfaces are all initial indications of the upper snowpack deteriorating.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

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

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

Small solar triggered slides, cornice fall, or thin-spot triggering may overload a persistent weakness buried 100 cm deep. This could lead to surprisingly large avalanches.

Carefully evaluate big terrain features by digging and testing on adjacent, safe slopes.>Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Apr 3rd, 2013 2:00PM