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Avalanche Forecast

Archived

Mar 1st, 2013–Mar 2nd, 2013

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

Regions

Purcells.

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

As an upper trough moves towards the California coast cutting off the moisture supply of the pineapple express. This will reduce accumulations and winds over the region. Saturday: Light precipitation amounts accompanied by light-moderate ridgetop winds from the SW. Alpine temperatures near -2 and freezing levels rising to 1900 m in the afternoon with a moderate to high diurnal trends. Sunday: Light precipitation accompanied by moderate ridgetop winds from the NW. Alpine temperatures near -8 and freeing levels falling to 1000 m. Monday: No significant precipitation expected. Ridgetop winds will blow light from the South. Alpine temperatures -9 and freezing levels near 1300 m in the afternoon.

Avalanche Summary

A few skier triggered slab avalanches were  remotely triggered on Friday up to size 1.5, running far and fast. On Thursday, slab avalanches to size 1.5 were ski cut and failed naturally. Recent explosives testing in the southern portion of the region producing slab avalanches to size 2.5 isolated to the storm snow.

Snowpack Summary

Moderate amounts of new snow has fallen adding to an ongoing storm snow instability, particularly on the west side of the region where accumulations have been highest. The variably reactive February 12th and 15th surface hoar layers now exist up to 80cm below the surface and seem most prevalent on the west side of the region. This interface may also be reactive on solar aspects where a sun crust exists. A surface hoar layer buried on February 23 is still on the radar of some operators. This layer has been less likely to trigger by skiers, but may still be sensitive to large loads like avalanches in motion or cornice fall. The mid and lower snowpack are generally well settled and strong.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.