Synoptic and mesoscale influences on west Texas dryline development and associated convection

Drylines are common to the High Plains in the spring months, and are responsible for a significant percentage of the severe thunderstorm development observed during that time. The behavior of drylines is controlled by processes ranging over a wide spectrum of scales. The constructive and destructive effects of all these influences are still largely misunderstood, significantly hampering efforts to accurately forecast the existence and location of dryline convection initiation.

This study addresses many of the controls on dryline development and structure, and the initiation and subsequent intensity of deep moist convection. West Texas Mesonet (WTM) observations from the spring months of 2004 and 2005 have been used to quantify the existence and magnitude of dryline events in the southern High Plains over this time period. NCEP/NCAR upper-air reanalysis data, composited against these WTM-observed dryline cases, contribute significant insight into the synoptic forcing on the horizontal gradient in surface specific humidity (the true “strength” of the dryline), the amount of surface wind convergence, and the initiation and mode (supercellular vs. non-supercellular, tornadic vs. non-tornadic) of any eventual convective development. The study also highlights a number of lower-end cases that do not develop in commonly-considered locations with respect to synoptic features, forcing one to re-examine the true definition of a dryline in a few instances.

The Simultaneous Observations of the Near Dryline Environment (SONDE) project gathered mobile mesonet and Stick-net observations in close proximity to a number of drylines during the spring months of 2005 and 2006. These observations will shed light on the variability of the dryline environment on the scale of 1-10 km, particularly in the context of convection initiation, which occurred during SONDE sampling on a few occasions.