The cold front that passed through the region last week (2/22) brought 3” to 15” of low-density, very transportable snow primarily from Mammoth Lakes north to Virginia Lakes. The storm system was accompanied by periods of moderate to strong SW - S winds, veering to N - NE, which formed Wind Slabs and drifts primarily near treeline and above, near favored features on many aspects throughout the alpine. The temperatures have remained below seasonable norms since post-frontal passage, slowing the normal strengthening and bonding process. Fresh Wind Slabs will begin to form this afternoon into the evening near and above treeline as another storm takes aim at the Sierras with 3" to 12" forecasted this afternoon into the evening with moderate to strong SW winds. This will create a new round of potentially tender Wind Slabs on NW-N-NE-E-SE aspects. Winds are forecasted to switch to the Northeast late tonight, which may further complicate the Wind Slab distribution, near and above treeline. As a result, additional caution is required in steep or complex terrain near and above treeline where recent drifting is evident. Wind Slabs will most likely be found in the upper elevations under cornices, below ridgelines, at the top of chutes and couloirs, and on steep convexities. Hollow sounding drifts, or dense cracking snow may indicate rider triggered failure is still possible.
If the approaching storm produces the upper snowfall amounts forecasted, we may see some Storm Slab concerns, near and above treeline, by tomorrow AM.
Below treeline, in very sheltered areas, the snow is mostly soft with thin Wind Slabs dispersed throughout and the occasional recently exposed old melt/freeze crust.
The patchy persistent weaknesses from early season that was primarily confined to NE-N-NW aspects above ~9500’ is showing signs of sintering and strengthening with test results show slowly improving cohesion. However, Thursday’s approaching storm is forecasted to produce up to 3’ of snow. 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, to step 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 coverage (below threshold).
