Avalanche Forecast

Archived

Mar 17th, 2016–Mar 18th, 2016

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.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Northwest Coastal.

Take a conservative approach when the sun is beating down or it feels balmy, especially if you're not sure about the existence and sensitivity of buried persistent weaknesses.

Confidence

High

Weather Forecast

FRIDAY: Mainly sunny. The freezing level should jump to around 1700-1900 m and ridge winds are moderate from the E-SE. SATURDAY: Increasing cloud with a chance of flurries. The freezing level dips to 1300 m but climbs back to 1700 m late in the day. Winds should be light. SUNDAY: A mix of sun and cloud. The freezing level is near 1800 m and winds are light or moderate from the east.

Avalanche Summary

There were numerous reports of natural and rider triggered wind slabs on northerly aspects and cross-loaded gullies on Wednesday. Most of these were small (size 1-1.5) with a few up to size 2. There were also reports of loose wet snow with the 20-40 cm of new snow moistening and sliding on a buried sun crust. In addition, a couple natural cornice falls to size 3 were observed with numerous cornice falls being reported in the past few days.

Snowpack Summary

We've seen variable amounts of new snow but an average of 30-40cm has accumulated over the last few days in sheltered areas. Variable winds have redistributed the surface snow forming wind slabs and adding mass to cornices. On south aspects, the recent storm snow may have buried a sun crust. Lower elevations and south aspects are going through daily melt-freeze cycles. A layer of surface hoar or melt-freeze crust buried on March 3 is down 70-100cm and has been recently reactive in the areas north of Stewart. An older crust/facet layer buried in early February can now be found down over a meter but this layer has been dormant for several weeks.

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.