Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Jan 2nd, 2012–Jan 3rd, 2012

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

Purcells.

Confidence

Good - -1

Weather Forecast

An approaching pacific frontal system will bring light -moderate precipitation to the region through Tuesday. Snow amounts 5-10cms. Ridgetop winds will be 35-55km/hr from the SW. Freezing levels may rise to 1000m. Wednesday: Snow amounts near 10cms. Ridgetop winds 45-55km/hr from the SW. Freezing levels could rise to 1850m then drop to valley bottom Thursday. Thursday: Snow amounts 5-10cms. Winds light from the SW. Freezing levels drop to valley bottom.

Avalanche Summary

Over the past 48hrs a large natural cycle up to size 3.5 occurred. These avalanches ran on all aspects, and was evidence of a widespread storm cycle. Most operations proceeded with full avalanche control missions using explosives. They reported numerous large avalanches size 2-3.5 on N-NE aspects. I suspect that human triggering is likely out there creating large, destructive avalanches that may not be survivable. I would also avoid slopes with cornices overhead. They provide a substantial trigger that will very likely initiate a slide on the slope below.

Snowpack Summary

The Purcell region has seen up to 140cms since the Christmas holiday. The new snow has settled into a cohesive slab, and the average total snowpack depth is near 200cms. The ridgetop winds have consistently blown from W-SW and have redistributed the storm snow into wind slabs. Wind slabs are widespread and found in exposed alpine and treeline locations. Even open areas below treeline are suspect for wind affected snow. In sheltered areas the snow surface is starting to form surface hoar crystals (feathery), and surface facets (sugary crystals). These crystals may create a weak layer in the snowpack once buried. Below the surface down 80-140cms lurks the mid-December surface hoar/ crust, facet layer. This is a layer of concern. It continues to be sensitive to the weight of a skier or sledder. The recent load of new snow has also awoken the basil weakness near the ground on north facing slopes. This mixed bag of weaknesses has made for a very tricky avalanche situation as evidenced by the numerous accidents in the area over the last few days.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.