During the evening transition period, pronounced nocturnal cold-air intrusions on the eastern sidewall of the valley are observed. A regional-scale cold-air flow from the north of the valley is channeled through the gap between the Inyo and the White mountains. The flow discharges down the steep eastern sidewall as a strong katabatic current, overshooting the altitude corresponding to its neutral buoyancy. Gravity waves are generated across the valley as the intruding cold-air restores to its equilibrium position in the middle altitudes of the valley. The resulting cross-valley flow creates strong directional shear against the down-valley flow in the lower layers of the valley atmosphere. Shear instability leads to breaking Kelvin-Helmholtz waves at the two-layer interface, resulting in vertical turbulent mixing across the depth of the valley. Later in the night, a nighttime warming episode observed with field measurements at the valley floor is reproduced with good magnitude and temporal precision. This warming as a result of flow transition from down-slope (from the western sidewall) to down-valley flow is well-resolved on the fine LES grid.
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