Challenges in modelling and forecasting radiation fog with atypical dissipation during the night: a case study at Zagreb Airport

Fog continues to intrigue scientists because it is complex and often unpredictable. In this study, we unravel the intricacies of an unusual fog event at Zagreb Airport in December 2015. Contrary to conventional wisdom, fog dissipated at an atypical hour. The research presented here addresses the fundamentals of this fog event using a multidisciplinary approach that merges observational data with numerical modeling techniques. Through careful analysis, the interplay between microphysical processes, mesoscale dynamics and synoptic forcing (the latter becoming stronger at the end of the event) responsible for the formation and dissipation of fog is revealed. Analyzing such events is valuable because extremes can offer quality insight into the behavior of fog. The results provide a description of the evolving nature of fog, from its onset to its dissipation into mist. Visibility fluctuated throughout the event, providing insight into the underlying atmospheric processes. In addition, the numerical WRF simulation provided invaluable insights into the evolution of the fog event, highlighting the crucial role of vertical wind motion (the w-component of wind) in the lower troposphere in triggering fog dissipation. Despite some deficiencies, the simulations accurately reproduce the spatial distribution of the cloud water mixing ratio during fog onset and dissipation. This parameter, together with the vertical wind motions, was identified as the most reliable predictor for the onset and dissipation of fog and offers promising opportunities to improve fog forecasting.