Avalanche Forecast

Issued: Mar 27th, 2013 11:00AM

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

swerner, Avalanche Canada

Purcells.

Be aware of changing conditions with daytime warming and sunny skies. Watch solar slopes and overhead hazards.

Summary

Confidence

Good

Weather Forecast

A split-flow pattern will be keeping things fairly benign; the most significant change through the forecast period will be warmer temperatures (above seasonal norms), higher freezing levels and intense solar radiation. The region will likely see more cloud cover come Friday.Thursday:Â Few clouds. Alpine temperatures near 1.0 degree. High diurnal temperature swings up to 2100 m in the afternoon. Ridgetop winds will blow light from the West.Friday: Scattered cloud cover. Alpine temperatures near 2.0. Freezing levels 2100 m and ridgetop winds light from the West.Saturday: Few-scattered cloud clover. Alpine temperatures -4.0 and freezing levels 1900 m. Ridgetop winds light from the West.

Avalanche Summary

On Tuesday, numerous solar induced slab avalanches and loose wet avalanches occurred. The largest being size 2.0 from higher elevations on West and South aspects. Many loose wet avalanches initiated from steep solar slopes up to size 1.5. Expect this type of avalanche activity to persist through the forecast period. Additionally, large natural cornice releases, or other heavy human triggers, triggering very large slabs remain.

Snowpack Summary

Surface faceting and surface hoar growth has been prevalent on shady slopes and at upper elevations, while the surface snow on sun-exposed slopes and at lower elevations has been subject to daily melt-freeze cycles. Cornices are reported to be very large and weakly bonded. Wind and storm slabs are reported to be strengthening, but may continue to be sensitive to human-triggers. The weak layer of buried surface hoar sitting on a crust down around 70-120cm, and has been producing variable but sudden results in snowpack tests. This deep 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. Slopes with corniced entrances, or exposed to cornice falls should be avoided with these conditions.

Give cornices a wide berth when travelling on or below ridges.>Cornices become weak with daytime heating, if they fail, they could trigger large, deep slabs on the slopes below.>

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

2 - 5

Persistent Slabs

Small solar triggered slides, cornice fall, or thin-spot triggering may overload a persistent weakness buried near 100 cm deep. This could lead to surprisingly large avalanches. Wind slabs linger on lee slopes and cross-loaded terrain features.

Dig down to find and test weak layers before committing to a line.>Plan escape routes and identify safe zones before committing to your line.>Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Loose Wet

Expect to see wet loose snow avalanches out of steep rocky sun-exposed slopes. 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: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Valid until: Mar 28th, 2013 2:00PM