FOG FORECASTING FOR THE SOUTHERN REGION - A CONCEPTUAL-MODEL APPROACH

The prediction of fog occurrence, extent, duration, and intensity rema ins difficult despite improvements in numerical guidance and modeling of the fog phenomenon. This is because of the dependency of fog on mic rophysical and mesoscale processes that act within the boundary layer and that, in turn, are forced by the prevailing synoptic regime. Given existing and new technologies and techniques already available to the operational forecaster, fog prediction may be improved by the develop ment and application of a simple conceptual model. A preliminary attem pt at such a model is presented for the southern region of the United States (gulf coastal states) and requires information regarding cloud condensation nuclei, moisture availability (or saturation), and dynami c forcing. Each of these factors are assessed with regard to their ext ent and evolution with time. An illustration, and potential applicatio n, of how the model could be used is detailed as no extensive operatio nal testing has yet been completed. Instead, the model is applied in h indcast to verify its application. Successful use of the model will re quire an operational forecaster to assimilate all available tools incl uding climatology, numerical guidance, sounding analysis, model diagno stic software, and satellite imagery. These must be used to characteri ze and quantify the nature of the local and regional boundary layer in the forecast region according to macroscale forcing and moisture avai lability, the initial local settings and boundary layer, qualitative a ssessment of cloud condensation nuclei, and the interaction of these i n time and space. Once identified, the evolution of the boundary layer may be forecast with regard to the overall environment for fog occurr ence, its likely extent, intensity, and duration.