Avalanche Forecast

Archived

Mar 21st, 2017–Mar 22nd, 2017

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 unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Glacier.

We are entering a tricky Low Probability, High Consequence cycle. The reality is that large, likely un-survivable avalanches continue to occur sporadically and are very hard to predict. Manage your exposure and be conservative in terrain selection!

Weather Forecast

This week expect unsettled weather. Today should be mainly cloudy, with isolated flurries and moderate S'ly winds. Freezing levels will rise to 1900m with an alpine high of 0'C. Overnight the flurries should accumulate to ~6cm. Wednesday will be similar with another 7cm expected and freezing levels to 1700m. On Thursday expect a few sunny breaks.

Snowpack Summary

In the last week a series of storms dumped over 150cm of heavy snow (rain below 1700m), with extreme winds (100+km/h) and warm temps. Overnight the winds shifted to N'ly, and are now reverse loading lee slopes. Below ~1700m a rain crust caps a moist and weak upper snowpack. The cornices are huge and have been failing providing a large trigger.

Avalanche Summary

The snowpack has demonstrated it's potential to produce very destructive avalanches. For example, on Sat Macdonald West Shoulder avalanched naturally ripping out mature timber and running to the valley floor. Sporadic avalanches continue to occur, like this one yesterday in the Smart drainage, showing wide propagation and multiple step down layers.

Confidence

Due to the number of field observations

Problems

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.

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.