Northern San Juan
AvalancheAmy Pertuz · Feb 11, 2021 · Northern San Juan
Weather
Bluebird day with mild temps and steady Westerly breezes near and above TL in the AM. Winds tapered off by early afternoon. Cloud cover came in the late afternoon and did not create any greenhouse effect on the snow. Moist surfaces seen on lower elevation sunny slopes, though most slopes above 10,700’ held onto dry surface snow.
Snowpack
Recent surface snow was light, low density, and undisturbed by wind effect below tree line. Moderate to strong AM winds out of the West were creating fresh windslabs on E aspects above tree line, and stiffening surface snow at tree line. We experienced some cracking and whumphing as we encountered this wind affected snow at tree line on a NE aspect, and were able to intentionally trigger small 0.5 windslabs 40cm deep there. On other aspects travelled the layer of concern is consistently about 60cm below the surface where a large grained facet layer from mid January has been producing hard but consistent and propagating failures on ECT. This weak layer has a 1F slab over it which has made it difficult to affect, but the clean cash-register drawer failures in large column tests is a bit disarming. ECTP 26 an E aspect NTL 58cm deep, and ECTP 24 on a NW aspect NTL 62cm deep.
Avalanche
Near and above tree line East aspects looked ripe and we intentionally triggered two small windslabs on a NE aspect at tree line. Both failed on a hard wind layer below the recent snow and did not fail on the deeper layer of concern. SS-ASr-R1D0.5 SS-ASc-R1-D0.5