Convective significant meteorological advisory (SIGMET) climatology

A climatology of convective sigmets issued by the AWC from January 1999 through July 2004 has been conducted over the CONUS and surrounding coastal waters. The climatology illustrates the variation of CSIG frequency and because CSIGs deny airspace, the climatology illustrates monthly, interannual, and diurnal impacts on air traffic and its flow management.

The climatology captures most convection. This was confirmed when CSIG climatology was compared to the Bothwell (1998) lightning climatology. In addition, the geographical locations of peak CSIG times compare favorably with the diurnal peaks of convection produced by Rasmusson (1971).

The annual march of CSIG-defined convection shows the northward and westward expansion of convection during the spring, the development of maximum convection over the southeastern CONUS and the Desert Southwest during the summer monsoon, and the rapid contraction of convection over the CONUS and shifting of convection to just off the Gulf coast during autumn. Interannual variability of CSIG frequency during six Julys shows how variations in the large-scale circulation impact the location and frequency of CSIG-defined convection. Analysis of diurnal variations of CSIG convection illustrate the different dynamic and thermodynamic processes that generate convection across the CONUS during different times of the day such as land/sea breeze interaction, destabilization through diurnal heating, synoptic systems, mesoscale boundaries, orographic effects, and the nocturnal low-level jet.