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Avalanche Forecast

Mar 23rd, 2013–Mar 24th, 2013
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
1: Low
The avalanche danger rating below treeline will be low
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
1: Low
The avalanche danger rating below treeline will be low
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
1: Low
The avalanche danger rating below treeline will be low

Regions: South Columbia.

Very large cornices have been falling off naturally and triggered by people moving near them. Expect cornices to continue to fall during this period of sunny weather.

Confidence

Good

Weather Forecast

Overnight and Sunday: Some convective energy may cause localised flurries with little accumulation overnight. Convective energy should be reduced on Sunday as the High pressure system moves over the Interior. Expect mostly sunny skies with light Southwest winds and freezing levels rising to about 1300 metres. Strong solar radiation may cause moist snow up to 2100 metres on Southerly aspects.Monday: The surface ridge of High pressure should stay mostly intact as it slides a bit to the East. Expect mostly sunny skies with light Southwest winds and freezing levels rising to about 1400 metres.Tuesday: Some cloud is expected to drift into the interior from a weak disturbance on the coast. There is a chance of flurries that may accumulate a couple of cms.

Avalanche Summary

A skier accidentally triggered a large cornice failure on approach to a Northeast aspect in the alpine in The Selkirks outside the boundary of a ski area, the cornice entrained snow in the track and then released a slab avalanche on the fan. There were several natural cornice failures in the Selkirks and the Monashees, and also a couple of small dry wind slab releases from alpine elevations in both mountain ranges.

Snowpack Summary

Cornices are reported to be very large and weakly bonded. Natural cornice falls are a concern during daytime warming. Cornices may also be triggered easily by travelling near them. Slopes with corniced entrances, or exposed to cornice falls should be avoided with these conditions. Dry windslabs may be found on Northwest thru Northeast aspects at higher elevations. These wind slabs are reported to be improving their bond to the old surface, but may continue to be triggered by skiers and riders. Loose moist or wet snow may fall naturally out of very steep terrain on sun exposed slopes. Small loose snow avalanches may trigger the recent storm snow slab where it is moist from solar heating and sitting on a planar sliding surface like an old sun or rain crust. The weak layer of buried surface hoar from March 10th is down more than a metre in most places, and is reported to require hard forces to result in resistant failures in snow profile tests. The lower snowpack consists of well bonded layers that are well settled and strong.

Avalanche Problems

Storm Slabs

Recent storm slabs and wind slabs may continue to be triggered by light additional loads. Periods of strong solar radiation may cause loose moist or wet snow to fall out of very steep terrain.
Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 4

Cornices

Recent cornice growth is very large and weakly bonded. Large cornice falls may occur naturally or may be triggered by people travelling near to them.
Do not travel on slopes that are exposed to cornices overhead.>Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine.

Likelihood: Likely - Very Likely

Expected Size: 2 - 6

Persistent Slabs

The March 10th weak layer of surface hoar is buried down more than a metre in most places. Large loads like cornice falls may trigger this deeply buried weak layer.
Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 3 - 6