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Avalanche Forecast

Archived

Mar 5th, 2014–Mar 6th, 2014

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

Regions

Sea To Sky.

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

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.