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Avalanche Forecast

Archived

Mar 8th, 2017–Mar 9th, 2017

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

Regions

Little Yoho.

Avalanche control on Mt. Stephen and Mt. Field in Yoho, and Mt. Hector on Hwy 93N Thursday, March 9. No activities in these areas during that day.

Weather Forecast

Light winds and -10C at treeline with only a trace of snow for Thursday. Friday another pulse of snow (10-12mm) along the divide and increased alpine winds into the moderate to strong range.

Snowpack Summary

50-70cm of storm snow has developed into a storm slab that is reactive at treeline and above. This sits over a mainly settled snowpack, especially closer to the Wapta where 225cm was found at 1800m near Tak Falls.  In some areas there is a facet layer down 70-80cm below 2000m that has gained strength, and well bridged rounding facets below. 

Avalanche Summary

Over the last few days there have been many larger than expected avalanches to size 3 within the storm snow from avalanche control as well as naturals. Some have been seen to step down to the deeper weak layers.

Confidence

Due to the number of field observations

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.