The development of a shape factor instability index to guide severe weather forecasts for aviation safety

An instability index, called the shape factor (SF), for weather forecasting was proposed using temperature profiles from a NASA/LaRC-hosted web-page featuring NOAA Rapid Update Cycle (RUC) radiosonde data used for short-term weather predictions. The index of instability was predicated on the sign and magnitude of the gradient of the equivalent potential temperature. A training data set of temperature profiles was obtained for both clear and severe weather conditions and the SF index was computed. The data showed marked differences in the magnitudes of the shape factors for the two weather conditions. Calculations of SF were compared with the several well-established instability indices and there appeared marked agreement between the SF and these other metrics. It is being proposed that this new index could be used as a parameter for input to statistical weather forecasting models to enhance overall aviation safety and air traffic management efficiency. Of particular relevance is the fact that more comprehensive results can be garnered since the SF index is calculated from the entire temperature profile and not just from selected temperatures as is the case for other indices of instability. Copyright  2008 Royal Meteorological Society