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Avalanche Forecast

Archived

Jan 6th, 2018–Jan 7th, 2018

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

Lizard-Flathead.

Expect persistent slab avalanche activity to continue as snow consolidates and loading increases. Adopt a conservative approach in the coming days.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Occasional flurries with minor accumulations through the forecast period.SUNDAY: Cloudy with flurries (5 - 10 cm snow possible) / Light to moderate west wind / Alpine temperature -3 MONDAY: Cloudy with snow overnight, accumulation 3-10cm possible / Light southwest wind / Alpine temperature -3 TUESDAY: Flurries (2-5cm during the day) / Light to moderate southwest wind / Alpine temperature -4

Avalanche Summary

On Saturday, natural and explosives-triggered avalanches to Size 2.5 were reported near Fernie, primarily on north & northeast aspects between 1800m and 2100m elevation. On Thursday there was a report of a skier triggered Size 2 avalanche in Orca bowl involving a group of 11 with 4 people caught and partially buried. See here for details on the MIN. This avalanche occurred on a northeast aspect at 1975m and reportedly running as a windslab sitting on a crust. Additionally, there have been several natural avalanches between 1600m and 1800m on steep or open glades on all aspects. This is where the mid-December layer has been most active.

Snowpack Summary

10cm of new snow by Saturday morning (18mm water equivalent) and warming temperatures has added significant load to the snowpack and increased slab properties above weak layers (see below). A persistent weak layer buried mid-December is 40-70 cm below the surface. This layer can be found in a variety of locations, but most commonly between 1600m and 1800m and consists of crusts on south and west facing slopes and feathery surface hoar in sheltered areas at and below tree line. It has been producing sudden results in recent snowpack tests.At higher elevations, wind has modified the snow pack creating a stiffer snow on top of softer snow condition. The lower snowpack is generally well settled with a thick prominent crust that was buried near the end of November. This crust has generally been reported to be unreactive, however it is possible that it may have been the bed surface for a skier triggered avalanche that happened on Thursday (See Avalanche Activity section above for details).See here for a recent forecaster blog for a summary of the tricky conditions in the snowpack and strategies on how to work around a persistent slab problem.

Problems

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.

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.