Avalanche Forecast

Issued: Mar 3rd, 2014 8:45AM

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

jlammers, Avalanche Canada

Purcells.

Forecast snowfall amounts are highly variable throughout the region with the south expecting the highest accumulations. If overnight snowfall amounts are greater than 20cm, the actual avalanche danger may be higher than posted.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Overview: A series of disturbances are embedded in a west/southwesterly flow which will bring continued snowfall to the region. There is some model disagreement in the track of the systems; however, southern parts of the interior are generally expected to see the highest accumulations.Monday night: Up to 20cm of snow / Strong southwest winds / Freezing level at surfaceTuesday: Light snowfall / Moderate to strong westerly winds / Freezing level at about 700mWednesday: Up to 20cm of snow / Moderate southwest winds / Freezing level at about 1100mThursday: Light flurries / Moderate to strong southwest winds / Freezing level at about 1100m

Avalanche Summary

In the Dogtooth Range on Friday, skiers initiated a cornice fall which triggered a size 2.5 slab avalanche on the slope below. In the same area on Saturday a size 2 slab was rider triggered from a ridge crest. A size 2 natural slab avalanche was observed on Saturday further south in the region. The February 10th interface is thought to have been the culprit in all of these events.I would expect fairly widespread storm slab avalanche activity with ongoing snowfall and wind.

Snowpack Summary

In some areas over 40cm of new snow is expected to overlie weak surface hoar in sheltered areas, a sun crust on solar aspects and thin wind slabs in exposed terrain. Initially, these new accumulations are expected to react as a wind slab in exposed terrain. As the new slab deepens and gains cohesion by wind and warming, more widespread storm slab activity can be anticipated.There is ongoing concern for a mix of weak surfaces which were buried on February 10th. This persistent interface lies between 50 and 120cm below the surface, and includes surface hoar, well developed facets and a mix of hard surfaces which remain widespread at all aspects and elevations. Although natural avalanche activity has tapered-off at this interface, destructive avalanches are still a very real concern with ongoing reports of human triggering, whumpfing and sudden/easy snowpack test results. The mid and lower snowpack are generally strong and well consolidated. Weak basal facets exist in many areas, but triggering has now become unlikely.

Problems

Storm Slabs

Continued snowfall and wind will add to a developing slab which overlies a variety of potentially weak surfaces. Watch for increased slab reactivity in wind exposed terrain. In sheltered, steep terrain the new snow may react as a loose dry avalanche.

Be cautious as you transition into wind affected terrain.>The new snow will require several days to settle and stabilize.>Be cautious of sluffing in steep terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

A deep, dense slab overlies a variety of weak layers and is still touchy in some areas. Triggering this weakness would have nasty consequences, so don't let the lure of powder tempt you into big unsupported terrain.

Avoid areas with overhead hazard.>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

Possible - Likely

Expected Size

2 - 5

Valid until: Mar 4th, 2014 2:00PM