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Avalanche Forecast

Archived

Feb 5th, 2013–Feb 6th, 2013

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, 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 Columbia.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Wednesday: Today the region sits under a weakening zonal flow maintaining moderate-strong ridgetop winds from the West. An upper disturbance embedded in the flow will bring snow amounts 10-15 cm. Treeline temperatures steady -4 and freezing levels 1100 m falling to 700 m overnight.Thursday: Unsettled conditions continue, bringing light snow accumulations. Ridgetop winds will switch and blow from the SW. Treeline temperatures near -3 and freezing levels rising to 1200 m in the afternoon, falling to valley bottom overnight.Friday: Outlook shows surface and upper ridge building, bringing dryer conditions and valley cloud. Treeline temperatures near -7 and freezing levels hovering around 800 m. Ridgetop winds blowing moderate from the NW.

Avalanche Summary

Natural avalanche activity continues up to size 2, with a glide crack release size 2.5. Natural activity has occurred on most aspects, with sluffing from steep terrain features. Rider triggered avalanches up to size 2 continue to be triggered on the January 26th interface that is buried 40-80 cm below the surface at treeline and below treeline elevations. With forecast storm snow and wind transport these layers may become more reactive naturally under the new loads.

Snowpack Summary

Wind slabs continue to develop in the alpine and at treeline. New snow sits on a surface hoar layer that developed at the beginning of February (20-40 cm down) and a sun crust that has developed on steep Southerly aspects. At lower elevations a melt-freeze crust has formed due to the recent high freezing levels. The recent storm slab continues to be reactive on solar aspects where an old sun crust has been buried and at treeline and below on steep convex slopes that host preserved buried surface hoar at the January 23rd interface (between 40-80 cms down). The mid-pack is well settled and strong. There are a few locations that continue to find a well preserved surface hoar layer from early January that is buried down about 90-100 cms and has been less reactive.

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.