Southern San Juan
SnowpackChris Bilbrey · Mar 30, 2020 · Southern San Juan
Weather
Light snowfall and obscured skies in the morning transitioned to broken skies and scattered clouds. Additional accumulations were light and around an inch - drifting noted along ridge tops. Light west-northwest winds with moderate gusts kept temperatures cool despite the sun making an appearance. We found 2 to 5" of new snow in the last 24 hours above 10,000 feet and a trace to 1" below.
Snowpack
Snow surfaces below 10,000 feet were firm from strong surface re-freezes making for easy travel - boot penetration was only ankle deep in the morning. Those same snow surfaces softened by the afternoon and became punchy. Above 10,000 feet, snowfall during March has settled to a 30 to 40" thick slab sitting above the old February snow surface - this transition point is easily identified in snowpits. Hand pits on multiple aspects around 10,200 feet found new snow sitting above a 1" thick melt-freeze crust with cold, dry snow below. Higher in elevation, our snowpit on a northwest aspect found a F-4F-1F (top to bottom) slab sitting above weaker facets that developed during warm, dry weather in February. Near-surface facets that formed in between early-March storms were not reactive in Extended Column Test. However, we observed propagating failures in two test on 28 taps failing in February facets. Although this weak layer of concern took a lot of force to fail, a thick slab above weaker snow is a worrisome structure. Finding an areas of the slope where the overlying slab is slightly thinner might make triggering easier. As we climbed to treeline, the March slab was stiffer but slightly thinner most likely from more wind-shuffling. February facets below were harder and showed initial signs of rounding as compared to similar aspects below treeline. A couple small loose snow sluffs observed from steep terrain with short burst of sun but this problem did not get going today. Alpine winds were high enough to drift recent snowfall into shallow and generally harmless soft slabs below ridge tops and in cross-loaded features.