Avalanche Forecast

Issued: Mar 13th, 2014 9:53AM

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

bcorrigan, Avalanche Canada

Purcells.

The hazard may be higher than expected if temperatures go higher in the afternoon than forecast. For more insight into the current tricky conditions, see the latest:Forecasters Blog.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Synopsis: The ridge of high pressure begins to break down with incoming Pacific frontal systems.Â All parts of the region should receive precipitation in the next few days.Tonight: Cloudy, with a trace of precipitation in the forecast,Â freezing level at valley bottom. Ridge top winds light from the south west, occasionally gusting to strong.Friday: Cloudy with flurries, trace of precipitation, freezing level around 1700 metres, winds from the west- light ,gusting moderate to strong.Saturday: Cloudy with flurries,Â 5 to 10 cm of precipitation, freezing level around 1600 metres, ridge top winds light to moderate from the south west.Sunday:Â Cloudy, 10 to15 cm of precipitation in the forecast, freezing level around 1600 metres.

Avalanche Summary

Large natural avalanches are still being reported throughout the forecast area. Explosives control has also produced some quite large results in some cases with wide propagations running full path over 1600 vertical metres. Recently size 2.5 avalanche was triggered by snowboarders at 2600 metres on a south east aspect. Neighboring forecast regions have reported large avalanches initiating in the new storm snow, then stepping down to deeper layers, some running full path to the ground. Cornice failures triggering large avalanches have been reported.

Snowpack Summary

The recent snowfall has now developed into a dense slab. In some deeper snowpack areas 80 to 100cm of storm slab overlies a weak surface hoar and facet layer that has been preserved in sheltered areas. A buried sun crust exists on solar aspects and and touchy wind slabs have formed at tree line and above. On lee slopes these accumulations have been pushed into much deeper deposits by moderate to strong southwest winds. Warming has added cohesion to the slab and wider propagations are now being reported. With rising temps and solar radiation, moist snow surfaces have been reported into the alpine. Wet avalanches on solar aspects have also been reported. There is ongoing concern for a mix of weak surfaces which were buried on February 10th. This persistent interface lies between 60 and 160cm below the surface, and includes surface hoar, well developed facets and a mix of hard surfaces which remain widespread at all aspects and elevations. In parts of the forecast area, large destructive avalanches are still a very real concern with ongoing reports of natural avalanches running full path. Weak basal facets exist in many areas, but without a large load, triggering now is unlikely.

Problems

Storm Slabs

Rising temperatures make the possibility of triggering a surface layer more likely. A moving surface slab might step down to weaker deeply buried weak layers. Use caution in recently wind loaded terrain.

Be alert to conditions that change with elevation.>Be cautious as you transition into wind affected terrain.>Choose conservative lines and watch for clues of instability.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>The new snow will require several days to settle and stabilize.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Deep Persistent Slabs

Cornice hazard continues to be a concern . A mature cornice failure could produce enough load to trigger deeply buried week layers.

Avoid areas with overhead hazard.>Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.>Choose conservative lines and watch for clues of instability.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Mar 14th, 2014 2:00PM