Composite synoptic analyses were constructed of the upper and lower quartiles of dryline intensity, termed STRONG and WEAK, respectively. STRONG drylines were associated with a short-wave trough in the upper-level westerlies approaching west Texas, an accompanying surface cyclone over eastern New Mexico, and southerly flow over the south-central United States. This synoptic environment was favorable for enhancing the dryline confluence responsible for strengthening the dryline. In contrast, WEAK drylines were associated with an upper-level long-wave ridge over Texas and New Mexico, broad surface cyclogenesis over the southwestern United States, and a weak lee troughthe dryline confluence favorable for dryline intensification was much weaker. A third composite termed NO BOUNDARY was composed of dates with no surface airstream boundary (e.g., front, dryline) in the WTM domain. The NO BOUNDARY composite featured an upper-level long-waveridge west of Texas and no surface cyclone or lee trough. The results of this study demonstrate the important role that synoptic-scale processes (e.g., surface lee troughs, upper-level short-wave troughs) play in regulating the strength of the dryline. Once such a favorable synoptic pattern occurs, mesoscale and boundary-layer processes can lead to further intensification of the dryline.
Subsequent sorting of the days by the type of convective weather along the dryline (no clouds, cumulus, cumulonimbus, severe weather, tornadoes) shows the effect of the synoptic and mesoscale environment on the development of convection. A logistic regression model is constructed to predict the occurrence of convection along the dryline, given the large-scale conditions. This model shows for the first time in the literature that dryline intensity is a significant factor for the severity of subsequent convection.