Avalanche Forecast

Archived

Apr 9th, 2017–Apr 10th, 2017

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.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

North Columbia.

The new snow is on a steady stabilizing trend, but avalanche hazards will persist the longest in wind affected areas. Watch for solar exposure to rapidly undermine stability.

Confidence

High -

Weather Forecast

Monday: A mix of sun and cloud with isolated flurries and a trace of new snow. Light southwest winds. Freezing level to 1800 metres with alpine temperatures of -3.Tuesday: A mix of sun and cloud with isolated flurries and a trace of new snow. Light southwest winds. Freezing level to 1800 metres with alpine temperatures of -3.Wednesday: Cloudy with sunny periods. Light to moderate east winds. Freezing level to 1900 metres with alpine temperatures of -2.

Avalanche Summary

Reports from Saturday showed storm slabs releasing naturally from Size 1.5-2.5 as well as with ski cutting and explosives control. Crown fracture depths ranged from 30-60 cm and the activity was focused at alpine elevations.Reports from Friday showed storm slabs releasing naturally from Size 2-2.5 on north aspects in the Rogers Pass area. Smaller wind slabs (Size 1-1.5) released naturally and with ski cutting on west aspects northeast of Revelstoke. Numerous loose wet releases up to Size 2 occurred over the previous 24 hours.A report from Wednesday detailed a natural Size 3.5 deep persistent slab release that occurred on a northeast aspect in the alpine, just northeast of Revelstoke. It was triggered by a smaller storm slab that released above it due to solar warming.

Snowpack Summary

30-40 cm of new snow blanketed the region after a series of storms over the end of last week. The new snow buried a mix of old surfaces that include melt-freeze crusts at treeline and below and on solar aspects in the alpine. Fragile new cornice growth also occurred along ridgelines over the course of the week. Below the new snow interface, a number of storm snow and crust layers that formed over mid to late March appear to be well bonded. The February weak layers are now down about 170-220 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These deep weak layers produced large avalanches with cornice falls and other heavy triggers in late March and early April. They remain an ongoing concern and may be more likely to fail on southerly aspects during periods of strong solar radiation.

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.