The latest storm to impact the region will begin to move off to the east today (Tuesday) with a weak ridge forming before 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 ushered in another round of unseasonably cold weather, which will slow bonding and strengthening allowing the Wind Slab hazard to linger longer. The wide swings in wind direction, optimal wind speeds for snow transport, and plenty of transportable snow have increased the avalanche hazard to Considerable for all aspects, near and above treeline for the forecast period.
Caution – though unlikely, areas that have received the upper snowfall amounts forecasted with this most recent storm may see some localized Storm Slab concerns, near and above treeline.
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, which formed Wind Slabs and drifts primarily near treeline and above on all aspects. The temperatures have remained below seasonable norms since post-frontal passage, slowing the normal strengthening and bonding process. These older Wind Slabs are stubborn in nature to fail 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.
Below ~9,000’, natural and triggered releases are unlikely due to thin and well-anchored snow cover (below threshold).