Avalanche Forecast

Issued: Mar 9th, 2014 10:30AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Storm Slabs, Persistent Slabs and Loose Wet.

jlammers, Avalanche Canada

South Columbia.

The big storm may have passed, but elevated danger ratings will persist, especially with forecast warm temperatures. If the sun comes out, danger ratings may exceed posted levels.

Summary

Confidence

Fair - Freezing levels are uncertain

Weather Forecast

Monday: Light flurries with a chance of broken cloud / Light to moderate westerly winds / Freezing level at 1500mTuesday: Mix of sun and cloud / Light northwest winds / Freezing level at about 1500mWednesday: Mainly clear skies / Light to moderate southwest winds / Freezing level between 1800m and 2200m

Avalanche Summary

On Saturday an avalanche resulted in a fatality in the southwest corner of the region. More details will follow as they become available. On the same day, a fairly widespread storm slab avalanche cycle to size 3.5 had occurred.At the time of publishing on Sunday, observations were limited although a few persistent slab avalanches to size 3.5 were triggered naturally or remotely and were thought to have failed on the February 10th interface. On Sunday morning a size 4.5 natural slab avalanche was also triggered on the southwest face of Mt Cartier near Revelstoke. It failed as a dry slab (unknown interface) and entrained wet snow as it reached lower elevations.Â Based on the intensity of Saturday night's weather, I get the feeling this was just the tip of the iceberg. With better weather (and more observations) on Sunday we'll soon learn more about what was likely a widespread large to very large avalanche cycle.

Snowpack Summary

In some areas over 80cm of recent storm snow overlies small surface hoar in sheltered areas and a sun crust on previously sun exposed slopes. In wind exposed terrain these new accumulations have been pushed into much deeper deposits by generally moderate southwest winds. Wind and warming have also created an "upside down" storm slab which may be particularly touchy where it overlies the crust. Many slopes below 1850m saw rain over the weekend and the snowpack at lower elevations is now mostly saturated. At ridgetop cornices are large, unsupported and waiting for the right trigger.We're still seeing avalanches on a mix of weak surfaces which were buried on February 10th. This persistent interface lies between 100 and 200cm below the surface, and includes surface hoar, well developed facets and a mix of hard surfaces which remain widespread at all aspects and elevations. This deeply buried layer still has the potential to "wake up" and create very large and destructive avalanches. Possible triggers include a surface avalanche in motion or a cornice fall.For the most part, the mid and lower snowpack are strong and well consolidated.

Problems

Storm Slabs

Heavy snow, wind and warming have added to the destructive potential of a well developed storm slab. The slab may be particularly touchy on previously sun-exposed slopes where it overlies a hard crust.

The new snow will require several days to settle and stabilize.>Be cautious as you transition into wind affected terrain.>Be alert to conditions that change with elevation.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

The early February weak layer may be stubborn to trigger, but long fracture propagations may still result if a large force such as a storm slab in motion or a cornice fall steps down to the persistent weak layer.

Avoid convexities or areas with a thin or variable snowpack.>Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 7

Loose Wet

At lower elevations the snowpack has been saturated by rain, and warm temperatures are forecast to persist. Watch for pushy loose wet avalanches in steep terrain below treeline.

Be cautious of wet sluffing in steep terrain.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Mar 10th, 2014 2:00PM