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Avalanche Forecast

Archived

Mar 9th, 2014–Mar 10th, 2014

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

Regions

Northwest Inland.

Confidence

Fair - Due to the number of field observations

Weather Forecast

Monday: Cloudy with a chance of flurries in the morning followed by a mix of sun and cloud. The freezing level is around 800-1000 m. Winds are moderate from the W-SW. Tuesday: Periods of snow – 5-10 cm. The freezing level is around 1200-1400 m and winds increase to strong from the SW.  Wednesday: Periods of snow. The freezing level is around 1000 m. Winds remain strong from the SW.

Avalanche Summary

Numerous natural (to size 2.5) and skier controlled avalanches (to size 2) were reported on Saturday. Most of these released on the recently buried snow surface, but some may have stepped down to the mid February layer. There was also a report of several remotely triggered avalanches.

Snowpack Summary

Around 20-50 cm of dense storm snow now sits on a layer of surface hoar and/or a thick layer of facetted snow on shady slopes at all elevations, a sun crust on steep solar aspects, and various wind affected surfaces in exposed terrain. Strong southwest winds have created dense wind slabs on exposed lee slopes and in cross-loaded features. The early February weak layer of facets, crusts, and surface hoar is buried down about 70-120 cm. There is no new info on this weak layer, but I suspect it remains active in many areas. Basal facets and depth hoar remain a concern in areas with thin or variable snow cover.

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.