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Avalanche Forecast

Archived

Feb 4th, 2013–Feb 5th, 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

Northwest Inland.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Tuesday: Expect clouds to develop, with a chance of light flurries. Alpine temperatures should reach -7 with light to moderate south-southwesterly winds.Wednesday & Thursday: Clouds persists with flurries tapering through the forecast period. Winds continue to be light from the southwest with alpine temperatures reaching -7 each the afternoon.

Avalanche Summary

Isolated windslabs up to size 2.0 have been controlled at ridgecrest and loose wet sluffing has been observed below 1200m.

Snowpack Summary

Wind slabs have built on lee slopes and behind terrain features likes ribs and ridges. In some locations up to 50 cm of new snow has buried a variety of old surfaces including old wind slabs, scoured thin slopes, crusts and surface hoar. This interface has shown isolated reactivity to rider triggering, especially around treeline and below treeline elevations. Recent warm temperatures have promoted some settlement and consolidated the recent snow into slab-like characteristics. With little observations from the field it's hard to get a good handle on how widespread this layer is, so I would  stress the importance of digging down to find and test weak layers. A cautious and curious approach is critical.The average snowpack depth at treeline is near 100 cm but remains quite inconsistent across the region. A strong mid-pack currently overlies a weak base layer of facets/depth hoar. Triggering of this basal weakness may still be possible from thin spots, rocky outcrops or under the weight of larger triggers such as cornice fall.

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.