Avalanche Forecast

Issued: Mar 5th, 2014 7:42AM

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

Peter, Avalanche Canada

Sea To Sky.

Summary

Confidence

Fair

Weather Forecast

Tonight and Thursday: Moderate to heavy snow – 15-30 cm overnight and another 20-40 cm during the day. The freezing level is around 1500-1600 m. Winds are strong from the S-SW. Friday: Mainly cloudy with flurries. The freezing level remains near 1500 m and winds are moderate from the W-SW. Friday night and Saturday: Moderate to heavy precipitation –up to 50 mm. The freezing level climbs to 1800 m and winds are strong from the SW.

Avalanche Summary

A few rider triggered and remotely triggered slab avalanches up to size 2 were reported on Tuesday, including one accidentally triggered wind slab that resulted in one full burial (fortunately the person was walked away unharmed). On Monday, numerous natural storm slab avalanches up to size 2 were reported. The common failure plane of these avalanches were within a storm snow (stellar crystal) interface sitting approximately 5 cm above the older surfaces of facets and crusts. Most of the recent avalanche activity has occurred on wind loaded features, primarily exposed north to east aspects.

Snowpack Summary

Strong southerly winds have redistributed some of the new storm snow on to leeward and cross-loaded slopes, building dense touchy slabs. Approximately 40-60 cm of storm snow sits on melt-freeze crust (with associated facets) that was buried at the beginning of March. The melt-freeze crust was found on all aspects at treeline and below, and on all but North aspects in the alpine. Recent snowpack tests give easy to moderate "pops" shears on this layer, and show potential for wide propagation. The very warm alpine temperatures and strong solar radiation from last week caused a great deal of settlement in the old storm slab above the early February weak layer. This crust/facet combo appears to be rounding and bonding in areas where the old storm slab is 150 cm or deeper. Shallow snow pack areas, where the weak layer is buried lass than 100 cm deep, continue to give sudden planar shears in snow profile tests. Big un-supported alpine North aspects are the most likely place to find a well preserved deeply buried February weak layer that may continue to allow for long propagations resulting in very large avalanches.

Problems

Storm Slabs

Heavy snow, strong winds, and mild temperatures will likely create dense new storm slabs. All this new snow is not bonding well to a melt-freeze crust buried at the beginning of March. Watch for loose wet avalanches below treeline.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Avoid freshly wind loaded features.>Stick to non-avalanche terrain or small features with limited consequence.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 4

Persistent Slabs

Heavy loading and rising temperatures could be enough to trigger the mid-February facet/crust combo, particularly on northerly aspects.

Use conservative route selection, stick to moderate angled terrain with low consequence.>Be aware of the potential for large, deep avalanches.>

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 6

Valid until: Mar 6th, 2014 2:00PM