Avalanche Forecast

Archived

Jan 22nd, 2012–Jan 23rd, 2012

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 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 on Tuesday

Weather Forecast

Monday: 5cm of snow / moderate southwest winds / freezing level at surfaceTuesday: moderate snowfall tuesday evening/ moderate to strong southwest winds / freezing level at 1300mWednesday: continued snowfall through early morning / winds becoming light and westerly / freezing level dropping

Avalanche Summary

Explosive-controlled wind slabs to size 1.5-2 were observed in the region in the past 24hrs.

Snowpack Summary

New storm snow from friday night/saturday morning has built up over wind slabs in exposed features and over loose dry snow in sheltered areas. New snow amounts from friday's pulse were highly variable throughout the region. Lesser 24hr snowfall amounts were at about 6-10cm on the east side, and up to 25cm on the west side. Anomalous southeast moderate winds were observed around Golden, so expect irregular loading patterns at ridge top in that area. The mid-December surface hoar/facet persistent weakness, now down around 55cm on the eastern side of the range and as deep as 190cm on the western side, is still causing operators concern, especially in shallow snowpack areas. Recent snowpack tests show moderate to hard, sudden planar results on this layer. The consequences of a failure on this layer would be large. Facets and depth hoar exist at the base of the snowpack. Cornices are large and weak in some areas.

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.

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.