A Lower-Tropospheric Thermodynamic Climatology for March through September: Some Implications for Thunderstorm Forecasting

Abstract

Abstract A thermodynamic climatology was constructed to investigate source regions of low-level moist airmasses and lower mid-tropospheric dry airmasses that contribute to the production of convective instability, and thunder-storms, over the United States. Mean monthly 1200 UTC values of potential temperature, mixing ratio, and geopotential height were computed at the surface and 750 mb for March through September (1966–1980) for 69 upper-air stations in the continental United States and Mexico. Analyses indicated that the Gulf of Mexico is the most significant source of low-level moisture east of the Continental Divide for all months, but the Atlantic Ocean also becomes a significant source in summer. The Gulf of California was found to be the most important source of low-level moisture west of the Continental Divide in summer. A distinct synoptic scale dryline was found over west Texas from March to June and analyses suggested that the strongest drylines occur in April and May. Northwest Mexico and the...