The interaction of a Pacific cold front with shallow air masses east of the Rocky Mountains

The study presented here describes the interactions that occurred between a n advancing Pacific cold front and shallow Gulf of Mexico and Arctic air ma sses situated east of the Rocky Mountains during the Verification of the Or igins of Rotation in Tornadoes Experiment (VORTEX) field campaign on 17-18 April over Oklahoma and adjacent states. These interactions were driven lar gely 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 experiment al 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 wi th in situ sensors and Doppler radars gathered data that allowed the author s to document the passage of a vigorous midtropospheric shortwave trough an d associated Pacific cold front, and the interaction of this front with the preexisting Gulf of Mexico and Arctic air masses. The Pacific front inters ected the ground to the west of the Arctic frontal boundary and dryline, an d subsequently rode over the top of the Gulf of Mexico and Arctic air masse s. This study also presents the detailed observational documentation of a d ryline-frontal merger by showing the merging or phasing of updrafts associa ted 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. I ts anomalous southward penetration into the VORTEX domain due to terrain-in duced blocking also played a role in producing severe weather.