Southern San Juan

Avalanche

Chris Bilbrey · Jan 21, 2023 · Southern San Juan

Weather

Single-digit temperatures in the morning only warmed into the low teens by the afternoon. Skies were sunny all day, but a lingering cloud deck was visible to the north. Northwest winds were steady enough for efficient snow transport near and above the treeline onto easterly slopes.

Snowpack

We traveled on multiple aspects across all elevations to get a feel for snow depths, depth to persistent weak layers (PWLs) of concern, and stiffness of the mid-body slab (aka holiday slab). In general, snow depths ranged 125 to 200 cm with southwest-facing slopes above treeline the shallowest. North and northeast-facing slopes were the deepest pushing north of 200 cm in most places (225 cm good average depth) up to 250 cm. Probing around, we found the PWL (11/29 drought facets) of concern around 125 to 150 cm deep sitting below a stout mid-pack slab that ranged 1F to P- (top to bottom). East aspects at upper elevations were deeper that west aspects, and probing across a west-facing slope above treeline yielded harder individual snow layers, but more discernable softer layers sandwiched between. Height of storm snow from 1/14 to 1/18 ranged 70 to 90 cm and increased in depth with elevation. In non wind-loaded areas, the most recent storm snow was right-side-up and supportive to travel - both skis and snowmobiles. Even when one of our machines got stuck, they never broke through the mid-body slab into weaker snow near the ground. Overall good bonding between the recent storm snow and the old snow surface or buried crust when using small test slopes and side-hilling with machines to test sensitivity. Drifted areas around treeline and higher seem like the places you could still trigger a slide near the surface. Walking above active loading slopes, we triggered several small, shallow wind-drifted areas on slopes around 35 degrees in steepness. No cracking or collapsing on our travels, and none reported to us by other riders in the area.

Avalanche

We observed a few slides that broke into old, faceted snow from November on northerly slopes and one small slide that likely failed in recent storm snow on an easterly aspect. Also, evidence of long-running loose snow sluffing on steeper easterly slopes above the treeline - likely from the last low-density snowfall on Friday, January 20.