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Avalanche Forecast

Archived

Dec 5th, 2012–Dec 6th, 2012

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

South Rockies.

Confidence

Fair - Forecast snowfall amounts are uncertain on Friday

Weather Forecast

Overnight and Thursday: Light snowfall / strong west winds decreasing to moderate and northwest by Thursday / Freezing level at surfaceFriday: Light snowfall / moderate to strong northwest winds / Freezing level at surface  (note: models are in disagreement regarding snowfall amounts for Friday. Amounts may be closer to 15cm)Saturday: Trace amounts of snow / Light west winds / Freezing level at surface

Avalanche Summary

I expect fairly widespread windslab activity in the wake of the strong winds and snowfall on Tuesday night.

Snowpack Summary

Recent storm accumulations have been highly variable throughout the region; however, some ares have seen moderate to heavy snowfall over the past few days. In general winds have been strong creating widespread windslabs at higher elevations. Warmer temperatures and rain at lower elevations have created moist surfaces that will most likely form a temperature crust with dropping freezing levels.At the base of the snowpack you may find the early November crust which is associated with a layer of facets either directly above or below.In general, snowpack data is sparse in this region and significant variations likely exist from one drainage to another. Digging down and making your own observations will be critical to safe slope selection. Any observations from the field are welcome at [email protected].

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.