Observations of the Relationship between 700-mb Temperatures and Severe Weather Reports across the Contiguous United States

The relationship between 700-mb temperatures and convective severe storm reports is examined using data from 1993 to 2006 for the contiguous United States. Severe storm reports are used as a rough “proxy” for the occurrence of deep moist convection, and spatial and temporal distributions of 700-mb temperatures associated with these reports are analyzed. Secondarily, the distributions are assessed by individual severe storm report type, and convective inhibition also is evaluated. The motivation for this study is derived from the occasionally used 10°–12°C at 700 mb rule of thumb for estimating the extent and strength of the capping inversion. Whereas there is a semblance of merit for using this rule at times, its utility is shown to be strongly dependent on 1) geographic location, particularly with respect to surface elevation and the frequency of elevated mixed layers, and 2) the time of year. Calculation of convective inhibition, careful examination of the sounding, and assessment of lifting mechanisms likely are more valuable than 700-mb temperatures when forecasting the potential for deep moist convection and severe storms.