The latest storm to impact the region (2/26) moved off to the east Tuesday with a weak ridge forming over CA briefly ahead of the next storm takes aim at the Sierras, Thursday thru Saturday. The latest storm deposited 3” to 6” (more in favored areas) of low-density snow and accompanied by unseasonably cold temperatures, which has slowed the bonding and strengthening process, allowing the Wind Slab hazard to linger longer from treeline and above. Below treeline, winds were not as strong, forming isolated Wind Slabs, primarily in exposed or open terrain. Wind Slab sensitivity is improving. Natural avalanches are unlikely but triggered releases remain possible from treeline and above through the forecast period. Well below treeline, natural and triggered releases unlikely.
The cold front that passed through the region last week (2/22) deposited 3” to 15” of snow primarily from Mammoth Lakes north to Virginia Lakes. The storm system was accompanied by periods of moderate to strong winds and significant wind-loading, which formed stiff Wind Slabs and drifts primarily near treeline and above on all aspects. The cold temperatures since frontal passage have slowed the normal strengthening and bonding process, especially where the Wind Slabs overlay near surface facets that formed prior. These older Wind Slabs are stubborn in nature but are not well bonded to the underlying snowpack. A large trigger (i.e. avalanche, cornice failure) may be capable of triggering these older Wind Slabs in isolated locations.
The patchy persistent weaknesses from early season, primarily confined to NE-N-NW aspects above ~9500’, continues to show signs of sintering and strengthening with test results indicating improving cohesion. However, Thursday’s approaching storm is forecasted to produce ~ 3’+ of snow. This will be the biggest storm since November to impact the region and may produce the biggest avalanche cycle of the season. If the upper amounts are realized we may see enough load to stress the underlying persistent weakness for it to become reactive or for slides, such as a large Wind Slab stepping down into the these deeper weaknesses.
Caution – the mid to lower elevation snow coverage remains thin with plenty of hazards lurking just below the snow surface (i.e. rocks, logs, and stumps). The snow is hiding plenty of hazards while providing little protection.