Avalanche Forecast

Issued: Apr 6th, 2012 10:18AM

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 Cornices.

Avalanche Canada ghelgeson, Avalanche Canada

Summary

Confidence

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

Weather Forecast

A stagnant weather pattern dominated by a ridge of high pressure brings increasingly sunny periods with benign convective cloud over the holiday weekend. Saturday: Freezing level starts at the surface, climbs to 1900 m, then returns to the surface overnight. Ridge top winds light out of the SW. Sunday: Flow switches from north to south late in the day allowing freezing levels to climb as high as 2000 m. Winds moderate East, switching S, SE Sunday night. Monday: Winds light S. Freezing level starts around 1000 m, climbs to 2000 m in the afternoon.

Avalanche Summary

Control work Thursday morning produced dry avalanches from size 1 - 2. Temps warmed up in the afternoon which produced a widespread solar induced cycle to size 2 on SW, S & SE facing slopes. Clear skies allowed for good visibility; one operator in the region observed evidence of an extensive natural cycle from April 3rd on S/SE aspects at and above treeline to size 3, failing on the March 26th crust/facet interface.

Snowpack Summary

The snow surface was introduced to the strong spring sun Thursday afternoon which left a crust in place on solar aspects, those that face SW, S & SE. Around 30 cm of snow fell Wednesday accompanied by moderate southwest winds which brings total snowfall since March 26th to 120 cm. This snow rests on a suncrust on solar aspects and a melt freeze crust on non solar aspects below 2000m. On N aspects, shears within the upper storm snow are tightening with the persistent warm temperatures, although a reactive layer down 40-50cm remains. The March 26 interface consists of a melt/freeze crust down around 100cm, on all aspects except true north treeline and alpine, where small surface hoar (5mm) is present in sheltered places. The bond at this interface is gaining strength, with lingering concerns on true south aspects where the crust is thickest and where the surface hoar lurks. At lower elevations, the consistent high freezing levels have kept the new snow heavy and moist. The deep, persistent early February surface hoar lingers in the snowpack giving sudden results in testing. Concern remains with heavy triggers (cornice), step down avalanches and rapid loading from intense precipitation, strong winds or sun.

Problems

Storm Slabs

An icon showing Storm Slabs
Two layers to watch: April 3rd, down 30 cm & Mar. 26, down 100 cm. I'd be wary of triggering the deeper layer on steep unsupported slopes, especially in places where the snowpack goes from thick to thin; near ridge crests and rock outcroppings.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 5

Loose Wet

An icon showing Loose Wet
Periods of sun are expected Saturday & the new snow will likely react to the strong solar input, producing loose snow avalanches, with the potential for deeper slab avalanches on slopes that bake all day under the strong spring sun.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Cornices

An icon showing Cornices
Cornices have grown large & unruly. Cornices receiving direct sun will eventually grow weak & there is potential for cornice fall to initiate deep persistent slab avalanches on underlying slopes. Pay attention to what's happening above you.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

3 - 7

Valid until: Apr 7th, 2012 9:00AM