Fine-scale orographic precipitation variability and gap-filling radar potential in Little Cottonwood Canyon, Utah

Fine-scale variations in orographic precipitation pose a major challenge for weather prediction, winter road maintenance, and avalanche forecasting and mitigation in mountainous regions. In this investigation we use ground-based X-band radar observations collected during IOP6 of the Storm Chasing Utah Style Study (SCHUSS) to provide an example of these variations during a winter storm in 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 central Wasatch Mountains. Precipitation during the weakly stratified prefrontal storm stage featured a wave-like barrier-scale reflectivity maximum over the Wasatch Crest and upper LCC that extended weakly westward along the transverse ridges flanking LCC. This precipitation pattern appeared to reflect a veering wind profile, with southwesterly flow over the transverse ridges but cross-barrier westerly flow further aloft. Sublimation within dry sub-cloud air further diminished low-level radar reflectivities over lower LCC. In contrast, the cold frontal stage was associated with stronger reflectivities over lower LCC and the adjoining north- to northwest-facing canyon wall, consistent with shallow, northwesterly upslope flow. These results highlight the fine-scale precipitation variations that can occur during winter storms in complex terrain and demonstrate the potential for improved analysis and forecasting of precipitation in LCC using a gap-filling radar.