Wind slabs can be found in south facing terrain features, and are expected to be bonding poorly to the underlying crust. Buried weak layers may be more reactive as temperatures rise Friday.
Conservative terrain selection and good travel habits are the best strategies to manage the deep persistent slab problem.
Northerly winds are expected to have developed fresh, reactive wind slabs in the alpine and treeline. These slabs are expected to form on southerly aspects and may bond poorly to the underlying crust.
With the sugary, faceted, and weak snowpack wind slabs could step down to the lower snowpack, resulting in larger than expected avalanches.
Weak crystals sit at the base the snowpack creating concern for large avalanches.
Whumpfing and cracking have been observed in many locations and human triggering should be considered possible on any steep slopes where snow becomes denser and forms a slab of cohesive snow.
On Wednesday small wet avalanches were reported out of steep and rocky features where solar impact is most significant.
As northerly winds are expected to continue to redistribute snow, natural and rider triggered wind slabs remain possible.
On Monday near Pemberton, a skier-triggered persistent slab avalanche occurred on a northwest aspect in the alpine. The bed surface of this avalanche was reported as a crust with large surface hoar above. Interestingly, this avalanche triggered a size 2 on a nearby slope, which failed on facets and depth hoar near the ground level. This avalanche is a sign pointing toward a developing deep persistent slab problem in this region.
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In exposed terrain at higher elevations, pockets of wind slab sit in wind loaded features while rocks may be exposed on others.
Large surface hoar has been reported on the surface in sheltered areas, with a crust present on solar aspects. Rising temperatures will likely break down surface snow and create a widespread crust below 2000 m once temperatures cool on Friday afternoon.
A layer of weak surface hoar sits buried around 20-40 cm deep. The upper snowpack is generally low density and weak. The mid and lower snowpack consist of crusts and facet layers, with depth hoar observed near the ground, which is very weak and highly uncommon for this region. These layers are the primary concern for this area.
The snowpack is currently weak and shallow for mid December. In deeper areas, snowpack depths only reach 100-130 cm.
Thursday Night
Clear skies with moderate northerly winds. Freezing level around 500 m.
Friday
Clear skies with an above freezing layer around 1500-2000 m. Moderate northwest winds. Alpine high of 0 °C.
Saturday
Mostly cloudy with 2 cm of snow possible. Light and variable winds expected. Freezing level below valley bottom. Alpine high of -10 °C.
Sunday
Partly cloudy with trace amounts of snow expected. Light and variable winds. Freezing level below valley bottom. Alpine high of -20 °C.
SaturdayMore details can be found in the Mountain Weather Forecast.
