Airborne Doppler analysis of a dryline-outflow boundary intersection and subsequent convection

The intersection point of a dryline and a baroclinic boundary (the “triple point”) is widely considered a favorable region for the development of deep convection. Primarily, this is due to larger values of convergence, which, if present over a relatively deep layer, can force air parcels up to their level of free convection before appreciable detrainment of moisture can occur. The wind profile to the northeast of the triple point often contains enough deep layer wind shear to allow convection to acquire supercellular characteristics, which includes the threat of tornadoes and damaging hail. For the above reasons, the triple point is carefully monitored for severe storm development.

Convective initiation in a triple point regime is quite complicated. Each individual boundary comprising the triple point has a characteristic vertical velocity magnitude and distribution. How these boundaries constructively (or destructively) interact largely determines the potential for deep convective initiation in a conditionally unstable environment.

On June 3, 1995, as part of the VORTEX mission, the Electra Doppler radar (ELDORA) on board the NCAR Electra aircraft collected pseudo-dual Doppler data on a dryline/outflow boundary triple point in the Texas panhandle. This triple point initiated several waves of convection in a periodic nature, some of which eventually became tornadic. These data provided a detailed look at the individual circulations associated with each of the boundaries, and also offered insight into the interaction process in the region of the intersection.

The presentation will introduce some theories on how convective initiation related to the interaction of the boundaries. Specifically, the presence of a residual dryline secondary circulation (RDSC) will be identified to the north of the outflow boundary. The ELDORA depiction of the initial evolution of a triple point storm (prior to attaining supercellular characteristics) will also be presented.