Ho Ho Hold Up! Hunting Persistent Slabs for Christmas

We had a lovely holiday in the Apgar Range looking for feedback from the persistent slab problem and monitoring the snow surface ahead of the incoming warm front.

• We did not see any recent slab avalanches on the west side of the peaks in the Lake McDonald area.
• On a southeast aspect at 5800 feet we were spooked by a slope-wide collapse as a weak layer failed below the surface. We triggered the collapse from the ridgeline which was rounded into a convex breakover with the slope getting steeper as it fell away from our feet.
• We got many propagating test results in snow pits. A few on northeast slopes failed 80 cm down from the surface both above and below the early December crust. We also got propagation on southeast, south, and southwest facing slopes where the snowpack was thinner and the crust was only buried about 40cm deep. These south-facing results were all within a very narrow elevation band, between 5500 and 6300 feet. Below 5500 feet the snowpack was too thin for there to be a slab above the crust. Above 6300 feet the slopes were scoured from previous winds.
• Ridgetop winds were from the southwest and generally light, with moderate gusts. We saw minimal blowing snow and the wind slabs we could find were very small and hard to trigger on test slopes.
• The new snow will fall on a variety of surfaces. We found preserved surface hoar on all aspects and elevations where we traveled today, as long as the slope was sheltered from the sun and the wind. We found a thin sun crust and moist snow on sunny slopes. Northerly terrain had firm (1F) wind drifts below ridges, and very soft, low density snow further down slope.

We stuck to planar or concave slopes less than 35 degrees that were free of convex breakovers and rocky areas so that we didn't have to worry about snow monsters lurking under our feet.