Avalanche Forecast

Issued: Apr 21st, 2014 9:15AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs, Loose Wet and Deep Persistent Slabs.

esharp, Avalanche Canada

Purcells.

Avalanche danger will be greatest in the band at and above treeline where rain falls on previously dry snow which may lie above an older crust.

Summary

Confidence

Poor - Due to the number of field observations

Weather Forecast

Synopsis: A southerly flow will generate widespread precipitation over the southern interior Tuesday and Wednesday before a weak ridge ushers in drier conditions on Thursday. Temperatures will remain warm through the first part of the forecast period.Tonight and Tuesday: Light to moderate precipitation - up to 15 cm of snow at upper elevations / Moderate south southerly winds / Freezing levels between 2000 and 2400m.Wednesday: Light flurries / Moderate westerly winds / Freezing levels falling to between 1500 and 1600mThursday: Sunny with cloudy periods and a chance of flurries / Light southwesterly winds / Freeing levels around 2000m

Avalanche Summary

Small slabs have been recently triggered naturally and by skiers in areas where the upper snow is moist and sits above a crust. At lower elevations and on solar aspects small to large loose wet avalanche continue to be triggered on steep slopes. Cornices collapses have been reported during periods of daytime warming. Occasionally these heavy triggers have caused large deep slab avalanches on the slopes below.

Snowpack Summary

Moist snow or a fresh crust may be found on the surface on slopes that have seen recent sun. Between 10 to 30cm of snow overlies several widespread melt-freeze crusts on all but high elevation North aspects. Wind slabs can be found in lee features on N and E aspects in the Alpine.Several persistent weak layers still exist in the highly variable snowpack of the Purcells:-The mid-March sun crust/surface hoar layer down 50-80cm and the early-March crust/facet/surface hoar layer down around 80-120cm seem to be laying dormant for the time being.-The mid-February crust/facet/surface hoar combo is typically down 60 - 120cm. Direct triggering of this layer has become unlikely, however, cornice fall, a smaller avalanche in motion or prolonged warming may wake this layer up. The resulting avalanche would be very large and destructive.- Weak basal facets can be found in many areas, however triggering this layer is unlikely.

Problems

Storm Slabs

Expect to see an increase in avalanche activity where rain affects previously dry snow. At higher elevations expect winds slabs will form on north aspects.

Avoid avalanche terrain during periods of rain.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Loose Wet

Expect to see an increase in loose avalanche activity were the forecast rain saturates the upper snowpack

Avoid slopes with glide cracks.>Avoid steep, open glades in the forest.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Deep Persistent Slabs

The potential for very large deep slab avalanches needs to remain on your radar. Cornice fall, warming temperatures or a smaller wet or wind slab avalanche in motion could act as triggers.

Be aware of the potential for very large, deep and destructive avalanches due to the presence of deeply buried persistent weak layers.>Pay attention to overhead hazards like cornices.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 6

Valid until: Apr 22nd, 2014 2:00PM