The Interaction of a Pacific Cold Front with Shallow Air Masses East of the Rocky Mountains

Abstract

The study presented here describes the interactions that occurred between an advancing Pacific cold front and shallow Gulf of Mexico and Arctic air masses situated east of the Rocky Mountains during the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX) field campaign on 17?18 April over Oklahoma and adjacent states. These interactions were driven largely by the complex topography of the region. Four air masses of distinctly different origin (i.e., Pacific polar, high-altitude continental, Gulf of Mexico, and Arctic), and the boundaries that separated them (i.e., Pacific cold front, dryline, and Arctic front), were observed within the experimental domain. This event produced more than $1 million worth of damage in the experimental domain due to severe weather. A dense network of ground-based in situ and remote observing systems and two research aircraft equipped with in situ sensors and Doppler radars gathered data that allowed the authors to document the passage of a vigorous midtropospheric shortwave trough and associated Pacific cold front, and the interaction of this front with the preexisting Gulf of Mexico and Arctic air masses. The Pacific front intersected the ground to the west of the Arctic frontal boundary and dryline, and subsequently rode over the top of the Gulf of Mexico and Arctic air masses. This study also presents the detailed observational documentation of a dryline?frontal merger by showing the merging or phasing of updrafts associated with the Pacific front and dryline and the subsequent development of a squall line. The behavior of the Arctic front is also explored in detail. Its anomalous southward penetration into the VORTEX domain due to terrain-induced blocking also played a role in producing severe weather.