CLOUD-TO-GROUND LIGHTNING AND UPPER-AIR PATTERNS DURING BURSTS AND BREAKS IN THE SOUTHWEST MONSOON

Convective bursts and breaks in the southwest U.S. monsoon are investi gated in a lightning context because cloud-to-ground (CG) lightning is an excellent indicator of deep convection. Bursts and breaks are iden tified using six years of Bureau of Land Management CG lightning infor mation. Composited upper-air analyses for 12 bursts and 10 breaks are developed to examine the synoptic-scale differences between these two regimes. Anomaly patterns are investigated, and average burst and brea k regimes are presented. This investigation shows the importance of mo isture, the location of the subtropical ridge axis, and the high-plate au thermal low. For the burst, the ridge axis is displaced northward a cross Arizona and New Mexico and moisture is usually abundant in the s outhwestern United States. During the break, the ridge retreats southw ard into northern Mexico, giving way to dry westerly winds across Ariz ona. The high-plateau thermal low is firmly in place during July and A ugust, and it pulls low-level moist air upslope into the Great Basin f rom the Gulf of California through the only opening available, which i s the lower desert of Arizona.