Avalanche Forecast

Issued: Apr 3rd, 2014 9:17AM

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

bcorrigan, Avalanche Canada

Purcells.

The hazard may be higher than forecast if snowfall amounts are larger than expected.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Synopsis: A slow moving frontal system will bring precipitation into BC.Tonight: Cloudy with flurries, some parts of the region may receive 20 to 30 cm of precipitation. No overnight freeze, freezing levels up to 1400m, Winds moderate, gusting to strong from the south west.Friday: Cloudy with flurries. Some parts of the forecast area may get up to 20 cm of precipitation. No overnight freeze and freezing levels may go up to 1600m. Winds moderate, gusting to strong from the south west.Saturday: Cloudy with flurries. 5 to 10 cm of precipitation in the forecast for the region, daytime freezing level around 1600m, overnight freezing level may drop to valley bottom in some parts of the forecast area, winds, light to moderate from the south west.Sunday: Cloudy with flurries. 5 to 10 cm of precipitation in the forecast, daytime freezing level around 1600m, no overnight freeze, winds, light to moderate from the south west.

Avalanche Summary

2 Reports of large natural avalanches on south east aspects and explosive testing is still producing large avalanches, ( size 2's and 3's) most stepping down to known persistent weak layers. We expect to see natural avalanche activity rise with snow and winds associated with the incoming storm system on Thursday and Friday, along with periods of sun and increased air temperatures later in the week.

Snowpack Summary

Up to 50cm of new snow has fallen in the central part of the region in the last storm, with lesser accumulations in the eastern part of the forecast region.. This new snow is settling well, but has also been formed into wind slabs on the lee sides of ridge crests by strong westerly winds.Numerous crusts can be found in the upper 60cm of the snowpack on south facing slopes. The March 15 crust/surface hoar interface is down approximately 50-80cm in most parts of the forecast area. At 90-120cm below the surface you may find surface hoar and crusts that were buried at the beginning of March. This interface is still touchy in some areas, particularly in the north of the region and continues to produce sudden planar failures in compression tests.The deeper facet/crust persistent weakness buried at the beginning of February, now down 120 - 200cm, has proven to be reactive and should not be trusted. An avalanche on any of these deeper, persistent interfaces would be large and destructive. Weak basal facets exist in many areas, but without a large load, triggering is unlikely.

Problems

Wind Slabs

Incoming storm with winds may build wind slabs on north and eastern lee slopes. Solar aspects can be tricky in the afternoon. Cornices are a big concern with rising temperatures and recent strong winds.

Cornices become weak with daytime heating, stay well back from corniced ridges>Use ridges or ribs to avoid pockets of wind loaded snow.>The new snow will require several days to settle and stabilize.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Deep Persistent Slabs

The February and March persistent weak layers could "wake up" if subjected to a large load ie: new snow, a cornice fall, or daytime heating on solar aspects.

Avoid convexities or areas with a thin or variable snowpack.>Be aware of the potential for large, deep avalanches.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

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