Avalanche Forecast

Issued: Apr 19th, 2013 10:34AM

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

swerner, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Due to limited field observations

Weather Forecast

An upper trough will move through the Interior tomorrow. The NW flow will bring cooler, dryer air to the region with some pulses of precipitation. Saturday: Overcast with some clearing in the most northern parts of the region later in the day. Light-moderate precipitation amounts. Ridgetop winds blowing moderate from the NW. Freezing levels near 1600 m.Sunday/Monday: A ridge of high pressure will bring a mix of sun and cloud, with cooling and dryer conditions. Freezing levels will be near 1200 m during the afternoon and falling to valley bottom overnight.

Avalanche Summary

No new avalanche activity has been reported.

Snowpack Summary

Up to 15 cm of new snow sits on a variety of old surfaces. These include melt-freeze crusts on solar aspects and dry snow with some surface facts and surface hoar on Northerly aspects. Wind slabs have built on lee slopes and behind terrain features. Cornices are huge and threaten slopes below.Deeper in the snowpack (60-120 cm down) a weak interface exists which consists of a crust on solar aspects, and surface hoar on high-elevation northerly aspects. Earlier this week, very large avalanches were reactive on this interface in the neighboring Glacier National Park. I would practice caution and remain suspicious of high alpine steeper slopes.

Problems

Wind Slabs

New snow and wind will likely build new wind slab problems at treeline and above. Large looming cornices exist on ridgelines and pose a threat to slopes below. Keep well back and watch your overhead hazards.

Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

A weak interface buried down about 60-120 cm has been creating surprisingly large avalanches in neighboring regions. Additional load by snow and wind may bring the slab above this layer closer to its tipping point.

Be aware of thin areas that may propagate to deeper instabilites.>Dig down to find and test weak layers before committing to a line.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 6

Valid until: Apr 20th, 2013 2:00PM