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Archived

Avalanche Forecast

Apr 5th, 2012–Apr 6th, 2012
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Kootenay Boundary.

Confidence

Good

Weather Forecast

Cool dry air out of the north brings light convective flow to much of the province Friday & Saturday. Friday: Sunny periods in the morning give way to broken cloud in the afternoon. Expect the occasional convective burst of snow. No significant precipitation is expected. Ridge top winds light out of the west. Freezing level tops out around 1700 m. Saturday: Freezing level starts at the surface, climbs to 1600 m, then returns to the surface overnight. Sunday: Flow switches from north to south Saturday evening resulting in slightly warmer temps Sunday. Freezing level climbs to around 2000 m. Winds light out of the east at treeline, moderate SW at ridge top.

Avalanche Summary

Wednesday's snowfall produced the usual direct action avalanches. Sluffing was rampant in steep wind sheltered terrain while upper elevation wind exposed slopes produced both natural and human triggered small soft slab avalanches to size 1. A size 3 avalanche was observed on an upper elevation SE-E facing slope that likely came out Tuesday. Previous to Wednesdays's storm the region was very active with avalanches. Natural, explosive and human triggered avalanches were reported up to size 2.5. Remote triggering has also been observed.

Snowpack Summary

Around 25 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. Reports from Wednesday afternoon indicate that the storm snow has been blown into soft slabs in upper elevation wind exposed terrain. 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.

Avalanche Problems

Wind Slabs

Wednesday's wind and new snow has been formed into wind slabs in lee start zones at ridge crest. A small wind slab event could step down to deeper more persistent weaknesses.

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

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 2 - 5

Cornices

Cornices continue to grow. There is potential for cornice fall to initiate deep persistent slab avalanches on underlying slopes. Cornices that receive direct sun will quickly grow weak. Pay attention to what's happening above you.

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

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 3 - 7

Loose Wet

Periods of sun are expected Friday & the new snow will likely react quickly to the strong solar input, producing loose snow avalanches.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 4