Avalanche Forecast

Issued: Mar 4th, 2014 8:53AM

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

swerner, Avalanche Canada

Sea To Sky.

My confidence in forecast precipitation amounts and timing is fair. If more then 20 cm of new snow accumulates by midday tomorrow, consider the danger rating in the alpine to be HIGH.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

A series of Pacific frontal systems will push through the region starting late Tuesday night into Wednesday. The second major low and warm front will hit Thursday. Rising freezing levels and moderate-heavy precipitation amounts are expected.Wednesday: Snow amounts 10 cm. Alpine temperatures near -3.0. Ridgetop winds 20 km/hr from the SW, gusting strong. Freezing levels 1400 m.Overnight Wednesday/ Thursday: Snow amounts near 10 cm overnight and possibly 10-15 cm through the day. Alpine temperatures -1.0. Ridgetop winds light from the SW. Freezing levels 1500-1800 m. Friday: Snow amounts near 5 cm. Alpine temperatures near -1.0. Ridgetop winds light from the South. Freezing levels 1500 m.

Avalanche Summary

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. With an increase in precipitation and rising freezing levels natural avalanche activity will likely continue.

Snowpack Summary

30-60 cm of new storm snow has buried the recently formed melt-freeze crusts and surface facets that developed last week. Strong southerly winds have redistributed some of this new storm snow on leeward aspects, building thicker and touchier slabs. The melt-freeze crusts were found on all aspects at treeline and below, and on all but North aspects in the alpine. 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. The February weak layer of crusts and facets has been reported to be rounding and bonding in areas where the old storm slab is 150 cm or deeper. Shallow snow pack areas where the old storm slab is closer to a metre or less continue to give sudden planar shears in snow profile tests. North aspects in the alpine may have had enough warming to settle the storm snow into a cohesive slab, but not enough to improve the weak layer bond. 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

Wind Slabs

Strong southerly winds are redistributing new snow onto leeward slopes (N-NE) building a thick, and touchy wind slab problem. Human triggers are likely. In sheltered areas, storm slabs have built and a poor bond exists to the mix of old surfaces.

Avoid freshly wind loaded features.>Minimize exposure during periods of heavy loading from new snow, wind.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Persistent Slabs

New load from snow, wind and warming could possibly trigger the deeper February layer. Human triggering also remains a concern. North aspects in the alpine are the most likely slopes to have a well preserved weak layer with a cohesive slab above.

Stick to simple terrain and be aware of what is above you at all times.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 5

Valid until: Mar 5th, 2014 2:00PM