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Avalanche Forecast

Archived

Mar 4th, 2014–Mar 5th, 2014

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

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.

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

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.