Avalanche Forecast

Archived

Apr 5th, 2012–Apr 6th, 2012

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Coast.

Confidence

Good

Weather Forecast

Friday: Unsettled conditions with scattered flurries and sunny breaks. Freezing levels around 1000m and light winds. Saturday: A ridge of high pressure is expected to keep things mainly sunny and dry. Freezing levels are expected to hover around 1200m, and winds should remain light. Sunday: Some increasing clouds with light precipitation later in the day.

Avalanche Summary

Reports from the Duffey Lake area on Wednesday include evidence of numerous natural slab avalanches up to Size 2.5 from Tuesday morning on northerly facing alpine and treeline slopes. Most failed within the storm snow but late March surface hoar was the suspected culprit for some deeper releases. One notable cornice-triggered 1.4m deep Size 3 occurred on the North Face of Joffre. Check out the telemarktips.com South Coast conditions forum for a report of a remotely triggered Size 3 slab avalanche on a north facing couloir in the east side of the Duffey Lake area on Sunday. The slab failed on basal facets and propagated 300m out of the couloir and wrapped around to the adjacent northwest.

Snowpack Summary

30cm of new snow in the Duffey Lake area in the past couple of days brings the total snowfall over the past week close to a metre, while rain followed by a skiff of new snow has resulted in dust-on-crust conditions in the Coquihalla area. The past week's snowfall overlies a predominately crusty interface, except north facing slopes at treeline and above where small surface hoar (5mm) may be found. Recent reports include hard but sudden compression tests results and a Rutschblock 4 whole block failure on this late-March surface hoar in the Duffey Lake area. Deep persistent weaknesses linger in many colder and shallower snowpack areas. Not only will daytime warming and sun-exposure cause surface snow to lose cohesion and cornices to weaken, they will also increase settlement rates and decrease slab stability.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.