Avalanche Forecast

Issued: Mar 4th, 2014 8:30AM

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

swerner, Avalanche Canada

South Coast.

New snow and wind are building a new storm slab that may not bond well to the old surface of crusts and facetted crystals. Check out the Forecaster Blog for more information on the persistent weak layer.

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. 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 -2.0. Ridgetop winds 20 km/hr from the SW, gusting strong. Freezing levels 1500 m.Overnight Wednesday/ Thursday: Snow amounts near 15 cm overnight with another 10-15 cm through the day. Alpine temperatures -1.0. Ridgetop winds light from the SW. Freezing levels 1300 m. Friday: Snow amounts near 5 cm. Alpine temperatures near -1.0. Ridgetop winds light from the South. Freezing levels 1500 m.

Avalanche Summary

Numerous natural size 2 slab avalanches were reported from the Coquihalla area on Monday. With an increase in precipitation and rising freezing levels natural avalanche activity will 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. Last weeks very warm temperatures and periods of very strong solar radiation 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 bonding in areas where the old storm slab is 200 cm or deeper (there is between 2-3 metres of snow above the weak layer in the Coquihalla area). Shallow snow pack areas where the old storm slab is closer to a metre or less continue to give sudden planar shears in snow tests (there is about 60-80 cm above the weak layer in the Duffey Lake area). 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

New storm slabs have developed and a poor bond exists to the mix of old surfaces. A thicker, touchier slab can be found on leeward (N-NE) slopes and behind terrain features. Avoid locations exposed to overhead hazards.

Good day to make conservative terrain choices.>Avoid exposure to avalanche terrain during periods of heavy loading from new snow, wind.>Avoid freshly wind loaded features.>

Aspects: All aspects.

Elevations: All elevations.

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.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

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