Observation Date: 12/30/2015
Traveled to Upper Slagamelt Lake using sleds via Twin Lakes road and Big Swamp Creek. Upper access is via Slagamelt Trail.
Mostly cloudy and cold in the am in the Big Hole valley. Surface hoar forming. Temperatures warmed at higher elevations past the inversion. Mostly cloudy with calm winds and light snow higher in the basin (8k+)
Evidence of significant wind loading from the west on the south face of Squaw mountain, cross loading the south facing paths.
New Snow: 0-3″
Only one avalanche observed and it was a few days old. An east facing slope (40deg) around 8200′ on the shoulder of one of the major paths had run to the ground, presumably on basal facets. Crown was ~300′ wide and ran 150′ (small shoulder slope) Wind loading was the likely culprit, no other signs of instability noted. Travel (sled) conditions were varied with a stiff to punchy slab sitting over facets lower in the snowpack.
Snowpit was dug around 8200′ on a 25 degree south facing slope near tree line before committing to crossing slopes higher in the drainage. Depth was 90-120cm with a meaty slab sitting on 2-3mm basal facets. CT17 failed on basal facets, and ECTP 26, 28. Decision was made to avoid shallower spots where we could still impact the slab. The snowpack was telling us it could could go big if we found the magic spot on the wrong slope. Snowpack in the upper basin was deeper 140-150cm but shared a similar structure. Overall decided to limit exposure to slopes over 30 degrees where deeper slabs connected to shallower areas.
Observer: NRCS Montana Snow Survey Lucas Zukiewicz