Southern San Juan
SnowpackChris Bilbrey · Jan 24, 2024 · Southern San Juan
Weather
Partly cloudy skies transitioned to on and off moderate snowfall late-morning. Around an inch of accumulations when it was said and done. Hardly any wind felt along ridgelines. By mid-afternoon, snowfall ended and visibility gradually improved.
Snowpack
The snowpack in the Lewis Creek drainage did not have the same supportive feel as places along the western side/ crest. January slab depths ranged 50 to 60 cm across elevation and aspects, and total snow depths hovering around a meter. Boot penetration was almost through the January slab at our snow pit location near 11,000 feet, stopping just above the January 4 faceted interface. This was on a west-northwest-facing slope. This main persistent weak layer of concern here is a 1F- layer of mixed faceted grains (mostly angular with some rounding) 1 to 3 mm in size. We observed multiple ECTPs failing with 26 and 28 taps at the above mentioned PWL, and Propagation Saw Tests (PST) propagated a failure to the end of the column after a cut length of 30/100 cm. Compression Tests (CT) decided to fail at a deeper, slightly softer faceted layer (closer to 4F) about 30 cm off the ground deck with sudden collapse results. These results occurred with 22 taps. We did not observe ECT failures at the deeper faceted layer. Westerly-facing areas close to ridgelines where the wind more effectively scours snow coverage/ depth had more bottomless/ trap door conditions. The snowpack here was about half the depth than lower down on slopes. Southerly aspects have a firm melt-freeze crust below snowfall from this week, and the new snow showed good bonding with ski pressure near treeline. We found the crust to be more robust on south and southwest aspects, and more breakable on southeast.