Avalanche Forecast

Issued: Apr 9th, 2014 9:44AM

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

swerner, Avalanche Canada

South Coast.

How does warming and solar radiation influence the snowpack? How do I manage cornice problems? Check out the new Forecaster Blog.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Thursday

Weather Forecast

An upper level ridge will keep the region fairly dry with a mix of sun and cloud through the forecast period. Thursday: Cloudy with sunny periods. The Coquihalla could see a possible temperature inversion, with alpine temperatures near 4.0 degrees. Ridgetop winds light from the West. Freezing levels near 1600 m. Friday: Cloudy with snow amounts up to 10 cm. Ridgetop winds moderate from the West. Freezing levels rising to 1300 m.Saturday: Sunny skies. Alpine temperatures rising to 8.0 degrees. Ridgetop winds light from the North. Freezing levels rising to 2000 m.

Avalanche Summary

Several natural wet slab (glide crack releases) were observed in the Coquihalla region at treeline and below treeline elevations. These avalanches were large up to size 3. Additionally, a size 2 wind slab was reported from a NE leeward open bowl at treeline. No new avalanche reports from the Duffy area. Natural avalanche activity may spike with periods of solar radiation on Thursday. Large, weak sagging cornices threaten slopes below if they fail.

Snowpack Summary

Up to 20 cm of new snow sits above a mix of surface hoar, facets and melt freeze crusts. The new snow seems to have a poor bond to old surfaces and isolated wind slabs likely exist. Surface snow has become moist on most aspects with the warmer temperatures and rising freezing levels. Large sagging cornices threaten slopes and could fail when the sun comes out.Snowpack tests have been producing hard resistant planar shears on the late March crust down 30-50 cm and the upper snowpack has strengthened.A couple persistent weak layers exist deeper in the snowpack. The March melt-freeze crust/surface hoar is reported to be down 60 - 100cm. The February crust/facet/surface hoar layer is now deeply buried down 150 - 250cm. These layers are mostly inactive at this time, but could re-awaken with extended warming, solar influence and large triggers like cornice fall.

Problems

Wind Slabs

Strong SW winds have set up isolated wind slab problems on leeward slopes, behind ridge crests and mid slope features like ribs/rock outcroppings. Sagging cornices may fail with warming and solar radiation. They could trigger the slope below.

Give cornices a wide berth when travelling on or below ridges.>Use ridges or ribs to avoid pockets of wind loaded snow.>Caution in lee and cross-loaded terrain near ridge crests.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Deep Persistent Slabs

Three buried weak layers exist in the snowpack. Deep releases have become rare; however, the weak layers could be activated by cornice fall, a surface avalanche in motion, or intense loading from wind.

Be aware of the potential for large, deep avalanches due to the presence of buried facets and surface hoar.>Large triggers like cornice fall could initiate a deep persistent slab.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 7

Loose Wet

With warmer temperatures, and sunny periods on Thursday, loose wet avalanches are likely.

Avoid slopes when temperatures rise and the surface snow becomes moist or wet. Signs of instability are pinwheels and natural avalanches. >Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

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