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Avalanche Forecast

Archived

Jan 6th, 2014–Jan 7th, 2014

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Rockies.

Confidence

Good

Weather Forecast

Tonight and Tuesday: A slight chance of precipitation with a weak upper disturbance passing through the region late Tuesday. NW winds becoming lighter in the afternoon with freezing levels at the surface.Wednesday: Another system is tracking through the region. Light precipitations are expected and winds should pick up again and blow from the W moderately. Freezing levels should remain at valley bottom. Thursday: Similar situation for Thursday as a more zonal flow is allowing frontal systems to move across BC. Precipitation amounts are still not certain but they look a little bit less than the previous system.

Avalanche Summary

We have had a vague report of an avalanche incident yesterday in which a skier triggered a size 2 slab avalanche on an E facing slope at top of treeline in an area in the N end of the Flathead. Yesterday, our field team also observed several natural avalanches up to size 3 in Elk Valley South out of steep alpine features some of which would have run to ground. In an area NW of Elkford, several large avalanches ran full path or close to full path on S and E facing slopes and left deep deposits on the trail. These would have occurred during or right after the storm.

Snowpack Summary

Today's moderate and strong winds from the SE most likely created more pockets of windslab on lee side below ridgetop in the alpine and at the top of treeline. I could see those being very sensitive to skier triggering. Cornices have probably grown since this wind event as well.  The storm slab is settling but is still sensitive to human trigger, especially where a weak faceted snowpack is underlying that top fresh layer. The facet/crust layer down 80-100 cm at treeline and below treeline  and the depth hoar layer in the alpine seems quite reactive on E aspects. Multiple recent natural and human triggered avalanches on this aspect is a good sign of that problem.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.