Fog clearing in the lee of an isolated, flat island: A fog shadow

This study investigates the phenomenon of fog clearing in the lee of Sable Island, Nova Scotia, termed a “fog shadow”, using observations from the 2022 Fog And Turbulence Interactions in the Marine Atmosphere field experiment and Coupled Ocean–Atmosphere Mesoscale Prediction System numerical weather prediction model. The fog shadow occurs when a shallow layer of marine fog dissipates downstream of this low-elevation island due to surface heating and turbulent mixing. Analysis focuses on two cases: July 24, 2022, when a fog shadow was both predicted and observed through multiple platforms, including satellite imagery, and July 26, 2022, when the model erroneously forecast a fog shadow. Though the model successfully predicted some fog shadow events, it consistently overestimated surface heat fluxes over the island, leading to excessive fog dissipation in forecasts. The study reveals that fog shadows can form when sufficient surface heating combines with turbulent mixing to erode shallow fog layers, though the precise mechanisms and conditions required remain to be fully understood. These findings highlight the challenges in accurately modeling air–sea interactions and fog evolution around small islands, suggesting several areas for model improvement, including enhanced resolution, better surface flux parameterizations, and more sophisticated turbulence schemes.