South Columbia

Date Issued: Friday, 18 February 2011 06:00 PM 
Valid Until: Monday, 21 February 2011 06:00 PM 
Next Update: Saturday, 19 February 2011 06:00 PM 

Purcells Danger Ratings
					Saturday 		Sunday 			Monday
Alpine 				3 Considerable 	3 Considerable 	3 Considerable
At Treeline 		2 Moderate 		2 Moderate 		2 Moderate
Below Treeline 		2 Moderate 		2 Moderate 		1 Low

Avalanche Problem: Wind Slab

Southwest winds built windslabs on North through East facing terrain in the alpine and open 
treeline.  As winds turn Northerly we may see reverse loading.

Avalanche Problem: Cornice

Cornices have grown large.  Cornice failure is its own hazard and can also act as a heavy trigger 
to slopes below.

Avalanche Problem: Loose Wet Snow
	
Steep, open sunny slopes below treeline may destabilize in the afternoon with the clear weather.

Confidence: Good, I am confident in the weather forecast.

Weather Forecast

Saturday & Sunday: Mostly sunny. Winds will turn to Northerly and temperatures could reach -5 in 
the afternoons. Monday: A mix of sun and clouds with the chance of light flurries.  Winds continue 
to be light and Northerly with temperatures reaching -5.

Avalanche Activity

Avalanche activity is slowing down, but we are still seeing reports of natural and rider triggered 
avalanches from both the South Selkirks and Purcells. These reports have been primarily windslab 
avalanches on North and Northeast aspects in lower alpine elevations, with the odd event at treeline.  
Surface sluffing at treeline is also common.

Heavy triggers (cornice falls and explosives) are triggering deeper avalanches to size 2.5 at the 
bottom of the recent storm snow.

One recent natural event in the Purcells released high on a North facing glacier and ran down into 
the valley bottom, redefining the runout zone and mowing down some big timber.

Travel Advisory

Areas of Concern:

    * Wind-loaded slopes (predominantly North through East) in the alpine and at treeline. 
	  Windslabs may be lower on the slope than normal due to the previous strong winds.
    * Convex rolls in open terrain.  
    * Slopes threatened by cornices.
    * Steep South facing slopes at lower elevations in the afternoon.

Techniques to Manage Risk:

    * Avoid wind slabs. You can recognize these by seeing wind furrows or waves on an otherwise 
	  smoothed over surface. If you're riding in wind affected snow, the snow will feel more dense 
	  and you may see cracking under your skis or sled tracks. Avoid wind slab on slopes steeper 
	  than 30º.
    * Drop in to your line or highmark well below ridgelines to minimize exposure to wind slab 
	  issues.
    * Protected planar slopes with even snow distribution are a safer bet.

Snowpack

Up to 60 cm of new snow fell in the last week and this snow has been heavily redistributed by 
initially strong and now moderate southwest winds.  Windslabs are present on lee features in the 
alpine and at treeline.  Storm shears are gaining strength, but poorer bonding is likely on steep 
south facing terrain where a buried suncrust lingers.  Below this the midpack is well consolidated.  
Deeply buried facets from November remain at or near the ground and, while mostly dormant, they can 
still produce deep destructive avalanches in isolated locations where the snowpack conditions are 
right (see Avalanche Activity).

Prepared by Matt Peter