Southern San Juan
AvalancheChris Bilbrey · Jan 8, 2024 · Southern San Juan
Weather
Sunny and cold. The north wind got after it today moving the plethora of snow off northwest to north-facing windward slopes onto lees. The wind made it feel even colder than the single digit temperatures.
Snowpack
We found on average 45 to 50 cm of new snow that fell in the last 24 hours, and between 70 and 80 cm since January 4. While snow depths are super impressive over a short period, the overlying slab is still quite soft. We traveled in the same area over the past two days, and sensitivity was remarkably less on Monday compared to Sunday. Conditions closer to touchy on Sunday was during a period of high PI in the afternoon. Inverted surface slabs was the name of the game today and where we found more reactive storm slab conditions - cracking, collapsing, and easy failures (only a couple of taps) 20 to 30 cm deep in hand pits. Some newly formed drifts were just shy of a meter deep in spots. Digging on wind-sheltered west and east-northeast slopes near and below treeline respectively yielded easy to moderate non-propagating failures in Extended Column Test (ECT). These failures occurred in a subtle change in storm snow around 15 cm below the surface (ECTN 7), and at the interface between the last two storms (ECTN 15). We also observed ECTNs around 20 taps in the weak facets (1-2 mm) that formed during the New Year dry period. This layer is between 10 and 20 cm thick. Compression Tests produced a mixture of Sudden Collapse, Progressive Collapse, and Break failures on similar layers of concern. The most noteworthy pit result/ occurrence was when we isolated an ECT on a west-facing slopes near treeline. Once we fully cut through the 5 cm K- hard wind-board below snowfall since January 4, a crack propagated across the column, and the entire block cash-drawered into our pit (ECTPV down 75 cm). Our main concern moving forward lies around slab settling and stiffening. With various layers of concern in the upper snowpack, rider-triggering may become more likely as the storm snow gains cohesion, or where today's wind ushered along the stiffening process. The step-down potential has returned to the avalanche menu, and deeper failures are a growing concern above a fairly intact mid-pack slab sitting above early-season snow.
Avalanche
Lots of long-running soft slab avalanches that likely ran during the last storm during periods of high PI. These were more or less across most aspects and elevations - highest concentration was near and above treeline. None broke very wide, but some ran close to or the extent of individual slide paths. None grew larger than a size 2, and most were in the size 1.5 range. No fresh natural Wind Slab avalanches visible from today's uptick in winds.