The objective of this study is to evaluate the capability of the Weather Research and Forecasting (WRF) model in simulating fog and visibility in local airports over the Korean Peninsula. A series of sensitivity experiments of the simulated fog to the horizontal resolution, surface layer, microphysics, and planetary boundary layer (PBL) processes in the WRF model is performed for a severe visibility event over the western part of the Korean Peninsula near Incheon on 9 February 2003. Also, the WRF model system is statistically evaluated for the 48-fog cases over Korea from 2003 to 2006. Based on the 4-yr evaluations, attempts are made to improve the simulation skill of fog and visibility over Korea by revising the statistical coefficients in the fog algorithm of the WRF model.

The results from the sensitivity experiments for a severe fog case indicate that an optimized physics setup in the WRM model including the WRF single-moment 6-class (WSM6) for microphysics and the YonSei University (YSU) PBL for vertical diffusion generally reproduces the occurrence and duration of the observed fog; however, it is also found that the simulated fog is highly sensitive to the design of model system such as the horizontal resolution and the height of surface layer, as well as the treatment of physical processes including the PBL and microphysics. A comparison of two existing visibility algorithms in the WRF model shows that uncertainties in the visibility algorithms add additional degree of freedom in accuracy of numerical fog forecasts over Korea. A revised statistical algorithm using a linear-regression between the observed visibility and simulated hydrometeors and humidity near the surface for 48-fog cases exhibits an overall, but not significant, improvement in the visibility forecasts at the airports in Korea.