Southern San Juan

Avalanche

Chris Bilbrey · Feb 24, 2020 · Southern San Juan

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Weather

Obscured skies and intermittent snow showers to start the day. Skies started to break late morning, gave way to scattered clouds by Noon, then clear skies by 1500. Temperatures remained cold even with afternoon sunshine. Winds were moderate along ridge lines with periods of strong gusts - around 1015, a prolonged gale force wind came down the main canyon that sounded like a 747 was trying to land. Followed by intense blowing and 70 foot tall trees leaning like twigs. Winds began to calm by late afternoon.

Snowpack

New snow totals range from about 1 to 2 inches below 10,000 feet, 2 to 3 inches between 10,000 and 11,000 feet, and 6 to 7 inches above that. Recent storm snow was predominately 4F and showed good bonding to a variety of old snow surfaces. Northwest to northeast-facing slopes below 11,000 feet still have the weakest upper snowpack structure with some places all facets to the ground. East to south-facing slopes below treeline continue to go through multiple melt-freeze cycles and are more supportable, but still have an generally weak structure only lacking a cohesive slab. Plenty of evidence exist of strong post-storm wind scouring isolated below treeline areas and forming thin drifts on leeward, micro terrain features. As we approached treeline, drifting was deeper but specific to areas below ridge tops. Strong winds contributed to erratic, upslope eddy effects in the near treeline band - parts of slopes scoured right next to places with drifts. Only minor sluffing noted on stepper, north-facing terrain near treeline. Alpine slopes looked smooth and phat from recent snowfall and moderate drifting. We expect wind-drifted slabs above treeline to be more widespread and sensitive than what we found in the near treeline zone. Digging on a southeast-facing slope near treeline revealed a 6 inch melt-freeze crust with moist facets (4F) below. We banged on this crust with lots of force and couldn't get it to budge, even after removing weaker snow from below. It seems like we still need a much bigger load to activate deeper persistent weak layers on east and southeast aspects at higher elevations in the La Plata's.

Avalanche

None observed today.