Fine-scale radar observations of orographic precipitation features during a Wasatch Mountain winter storm

Fine-scale spatiotemporal variations in orographic precipitation pose a major challenge for weather prediction in mountainous regions. Here we use ground-based X-band radar observations collected during IOP6 of the Storm Chasing Utah Style Study (SCHUSS) to provide an illustrative example of such variations during a cold-frontal passage over the Wasatch Mountains of northern Utah. Emphasis is placed on precipitation features in and around Little Cottonwood Canyon (LCC), which cuts orthogonally eastward into the Wasatch Mountains. This work also demonstrates the potential for improving weather analysis and forecasting of such variations in LCC using a gap-filling radar. Precipitation during the weakly stratified prefrontal storm stage of IOP6 featured a wave-like barrier-scale reflectivity maximum along the Wasatch Crest that extended weakly westward and upstream over the transverse ridges flanking LCC. These characteristics appeared to reflect a veering wind profile, which produced southwesterly flow over the ridges flanking LCC but cross-barrier westerly flow further aloft. Sublimation within dry subcloud air further diminished radar reflectivities over lower LCC. The cold front was associated with stronger reflectivities over lower LCC and at lower-to-mid elevations along the northwest-facing canyon wall, consistent with shallow, northwesterly upslope flow. Eventually, shallow precipitating cells developed in the moist-neutral postfrontal flow, with the depth, coverage and intensity of these cells increasing from over the Salt Lake Valley to upper LCC.