Spring is in full swing in the Sierras after a fast moving spring storm swept though the region Tuesday with 3” to 12” inches of new snow reported across the forecast area above ~8500’. Snow levels fluctuated considerably during the storm with many areas received rain Monday before turning to snow in the early morning hours on Tuesday. Snow levels rose once again Tuesday with rain up to almost 9,000’. Snow levels finally eased back down to ~8000 by Tuesday late afternoon. Loose wet avalanches were prevalent during the storm throughout the mid elevations. Upper elevations - strong southwest winds accompanying the storm formed Wind Slabs on leeward slopes above about 9,000’. Mammoth Mountain Ski Patrol reported significant results from avalanche control work on Wednesday morning. Most of these avalanches were triggered in wind slabs with small hand charges and ski cutting.
Westerly winds continued thru Wednesday and Thursday with snow banners and localized drifting observed from Mammoth south to Rock Creek, forming Wind Slabs throughout the upper and mid elevations, primarily on NW-N-NE-SE aspects. Since then, the Wind Slabs have had a couple of days to strengthen but moderate SW winds are forecasted for the mid to upper elevations today (Saturday), which may form very isolated shallow Wind Slabs in the mid to upper elevations on NW-NE-SE aspects where upwind fetches still have snow available for transport. Northwesterly aspects are starting to heat-up for the first time with the dry snow becoming wet for the first time, which will increase the possibility of loose wet avalanches. Rocky outcrops, gullies, and trees will trap the sun’s heat today and reflect in back down onto the snow, also elevating the hazard of wet sloughing. Large pinwheels or ski penetration of boot top or greater are signs the snow is loosing strength and becoming unstable. Starting early and being out of steep, rocky terrain before things get too warm is the best strategy for avoiding loose wet avalanches.
Caution - Firm snow conditions in the AM can produce slide-for-life conditions. A minor slide into hazardous terrain can have serious consequences.