Northern San Juan
AvalancheAmy Pertuz · Jan 29, 2021 · Northern San Juan
Weather
Moderate to strong Southerly winds but not significant blowing snow. Temps 20s with increasing clouds during the day.
Snowpack
The 65cm of recent storm snow has two weak layers within it (~20cm and ~40 cm below the surface) which is now covered in many places with windslab, and this is reactive to skier pressure as well as producing natural avalanches. The December 11 interface continues to be reactive in large column tests, though it is now deep and much harder to trigger. Another weak interface exists below the last week's storm snow, and was producing propagating results in ECT. Windslabs in the upper snowpack could step down into these deeper layers. Reactive snow was found on many aspects, but lower angle test slopes proved stubborn and remote triggering/ rumbling collapses were not observed today as much as yesterday. HS on an E aspect BTL was 140cm, with a mostly 4F bottom half of the pack, and a spicy layer cake of 1F windslabs mixed with F and 4F hard layers above that. Many areas below tree line have lenses of wind-affected snow after the last week's stout SW winds.
Avalanche
Evidence of a widespread natural cycle on many aspects from the last storm cycle. Fresh slides overnight appeared to have run in a mid-storm weak layer, estimated at 20cm below the surface, with some mid-storm events breaking deeper. A significant natural ran during the last storm on Red 2.5 NE aspect ATL, propagating across most of the bowl, likely triggered by windloading from recent SW winds. It appears to have broken in a deeper layer.