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Avalanche Forecast

Archived

Mar 22nd, 2013–Mar 23rd, 2013

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

Regions

Little Yoho.

Nice weather this weekend will tempt people to step out into bigger terrain.  Avoid steep, thin snowpack areas, especially East of the divide where triggering of large avalanches is possible.  SH

Weather Forecast

Light Northerly flow with weak convective afternoon buildup Saturday.  No new snow in the forecast and minimal solar effect with freezing levels up to 1600m.

Snowpack Summary

W of Divide: Generally well settled snowpack in deeper areas. Previous storm slabs buried by 20-40cm at TL and above.  Some whumpfing today at ridgetop in thinner areas on facets above Vermillion crossing.

E of Divide:harder wind slabs over a variety of surfaces from sun crust, facets, and depth hoar. Sensitive to human triggering in thin areas.

Avalanche Summary

Deep persistent slab avalanches have been occurring on basal facets this week. One such avalanche was remote triggered in the Observation Peak area and was up to 175cm deep. Click here for another avalanche on Redoubt Mountain (E of divide) from March 19th.  Obs. from Yoho today saw natural slabs up to 2.5 within the recent storm snow in the Alp.

Confidence

Due to the number of field observations on Friday

Problems

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.

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.