Gulf Region Techniques
(last updated 8/3/2005)
An examination of cold-season dense radiation fog development following two widespread rainfall events over the northern Gulf Coast (Maniscalco, Gary J., NOAA/NWS Forecast Office, Mobile, AL, 5/2002. Southern Region Technical Attachment, SR/SSD 2002-14)
This paper compares and contrasts two cases of cold season dense fog development during the evenings of January 12 and 14, 2002. Each event occurred in the wake of widespread rainfall. Regional rainfall distribution, surface and sounding data are examined in order to analyze the conditions prior to dense fog development. Surface visibilities fell below 1/2 mi each evening at both Mobile and Pensacola. This critical visibility value was not forecast in the 1800 UTC TAF for either station. Further, the visibility was not accurately forecast by the 1200 UTC NGM or AVN MOS guidance. The goal of this paper is to investigate reasons why both MOS and WFO forecasters failed to accurately forecast the visibility for each case.
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Numerical models of boundary layer processes over and around the Gulf of Mexico during a return flow event ( Birol, Kara B. A., J. B. Elsner, and P. H. Ruscher, 1998. Weather and Forecasting, Vol. 13, No. 4, pp. 921-933)
The return-flow of low-level air from the Gulf of Mexico over the southeast United States during the cool season is studied using numerical models. The key models are a newly developed air mass transformation (AMT) model and a one-dimensional planetary boundary layer (PBL) model. Both are employed to examine the thermodynamic structure over and to the north of the Gulf. Model errors for predicting minimum, maximum, and dewpoint temperatures at the surface during both offshore and onshore phases of the return-flow cycle are analyzed. PBL model forecasts indicate soil moisture values obtained from the Eta Model improve accuracy. It is shown that forecasts of maximum temperature for coastal locations are sensitive to the soil moisture used in the PBL model. The AMT model performs well in determining boundary layer parameters since it includes horizontal advective processes. The AMT model is also able to predict the regional differences caused by different surface forcing while passing over land or sea. Results lead to a strategy for making predictions during cool-season return-flow events over and around the Gulf of Mexico.
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Fog forecasting for the southern region: A conceptual model approach (Croft, P. J., R. L. Pfost, J. M. Medlin, and G. A. Johnson, 1997. Weather and Forecasting, Vol. 12, No. 3, pp. 545-556)
The prediction of fog occurrence, extent, duration, and intensity remains difficult despite improvements in numerical guidance and modeling of the fog phenomenon. This is because of the dependency of fog on microphysical 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 development and application of a simple conceptual model. A preliminary attempt 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 dynamic forcing. Each of these factors are assessed with regard to their extent and evolution with time. An illustration, and potential application, of how the model could be used is detailed as no extensive operational testing has yet been completed. Instead, the model is applied in hindcast to verify its application. Successful use of the model will require an operational forecaster to assimilate all available tools including climatology, numerical guidance, sounding analysis, model diagnostic software, and satellite imagery. These must be used to characterize and quantify the nature of the local and regional boundary layer in the forecast region according to macroscale forcing and moisture availability, the initial local settings and boundary layer, qualitative assessment of cloud condensation nuclei, and the interaction of these in time and space. Once identified, the evolution of the boundary layer may be forecast with regard to the overall environment for fog occurrence, its likely extent, intensity, and duration.
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A study of fog along the upper Texas coast (Kyle, Brian and Carolyn Levert, NWSO Houston, TX, 1998. Southern Region Technical Attachment, SR/SSD 98-19)
The purpose of this paper is to analyze sounding data to investigate possible correlations between low-level (surface to 700 mb) relative humidity and wind, and low ceilings and fog.
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