North Columbia Avalanche Forecast

Date/Time issued: Monday, March 16, 2009 at 4:00 PM
Valid until: Thursday, March 19, 2009 at 6:00 PM

Next Scheduled Update: Wednesday, March 18, 2009

---------- Cariboos ----------
				Tuesday 			Wednesday 			Thursday
Alpine 			3 - CONSIDERABLE 	3 - CONSIDERABLE 	3 - CONSIDERABLE
Treeline 		3 - CONSIDERABLE 	3 - CONSIDERABLE 	3 - CONSIDERABLE
Below Treeline 	2 - MODERATE 		2 - MODERATE 		3 - CONSIDERABLE

Confidence: Fair. 

Primary Concerns:

    * Persistent Slab: A variety of persistent weak layers (PWLs) lurking below the surface are 
	  primed for human triggering this week. Deeper PWLs may be harder to trigger but could act 
	  as step-down layers creating very large and destructive slides. 

    * Wind Slab: Moderate to strong southerly winds have created dense wind slabs behind ridges 
	  and terrain features at treeline and in the alpine. 

Travel Advisory   Issued: Mon, Mar 16 Next Scheduled Update: Wed, Mar 18

It continues to be difficult to predict when and where large avalanches might occur. This is due 
to an unusually shallow, weak, and complex snowpack with a variety of weak layers that are primed 
for triggering. In this situation it's best to stick to simple terrain, meaning low-angle forested 
slopes that are not threatened by overhead avalanche paths. Be particularly cautious near steep 
rocky terrain, areas that have not seen much use, and on unsupported slopes. Pay close attention 
to obvious clues of instability like whumpfing and cracking, loading by new snow and wind, and 
recent avalanches. If these signs are present then it is further evidence that a conservative 
approach is warranted. Sunshine and mild temperatures could be a factor on Tuesday. If so, avoid 
steep sun exposed slopes in the afternoon. 

Avalanche Activity   Issued: Mon, Mar 16 Next Scheduled Update: Wed, Mar 18

Numerous natural avalanches up to size-3 were reported on the weekend on all aspects, primarily at 
treeline and in the alpine. Most avalanches were failing on the early March suncrust or surface hoar 
layer, but several stepped down to deeper persistent weak layers or re-loaded bed surfaces from 
January. Several skier-triggered avalanches large enough to bury or kill a person were reported in 
Rogers Pass on Sunday. Natural avalanche activity should slow down early this week, but human-
triggered avalanches remain likely. 

Snowpack   Issued: Mon, Mar 16 Next Scheduled Update: Wed, Mar 18

Moderate to strong southerly winds have created pockets of dense wind slab in exposed N and E facing 
slopes at treeline and above. 40-70cm of new snow overlies a layer of facets or surface hoar on 
northerly aspects and a suncrust on southerly aspects. Easy and clean shears have been reported on 
the suncrust. The February 22 surface hoar layer is down approximately 100cm and is generally 
producing hard shears. The base of the snowpack is quite weak and consists of facets and depth hoar, 
especially in steep rocky terrain. 

Weather   Issued: Mon, Mar 16 Next Scheduled Update: Wed, Mar 18

Unsettled conditions will result in a mix of sun, cloud, and flurries for the next few days. Snowfall 
should be generally light with light to moderate southwesterly mountaintop winds. The freezing level 
should rise to 1000m during the afternoon. A series of disturbances is forecast to bring light to 
moderate precipitation from Wednesday to Friday with a gradually rising freezing level to 1500m by 
Friday. 

Issued by: Peter Marshall