Atmospheric rivers (AR) are episodic events that can advect relatively large quantities of moisture to Antarctica, contributing to both disproportionate precipitation and melting events. The Year of Polar Prediction (YOPP-SH), an international effort to improve weather prediction over the southern polar region, presents an opportunity to study the clouds and precipitation associated with winter AR events. This study uses enhanced surface, profile, and remote-sensing observations from the Antarctic Peninsula during a Targeted Observing Period near 16 May 20202, when an AR event occurred with characteristics similar to a warm front. We compare regional atmospheric simulations with the polar-optimized version of the Weather Research and Forecasting Model (Polar WRF) to various in-situ and remote-sensing observations. The study emphasizes data from three stations: Escudero, Vernadsky, and Rothera. Mixed-phase clouds were simulated at the three stations, with the precipitation being primarily rain at Escudero and primarily snow at Vernadsky and Rothera. The model produced reasonable simulations of the clouds and precipitation. Modeled longwave cloud forcing at Escudero well-matched observed values. A sensitivity test relaxing the hydrometeor concentration thresholds for secondary ice production indicates mixed-phase cloud sensitivity to the Hallett-Mossop process, especially at Rothera