Observations of supercell merger and tornadogenesis from May 4, 2003

The Pierce City, MO tornado of May 4, 2003 was notable not only for the loss of life it caused, but also for the series of supercell development, splitting and mergers that preceded the destruction. This sequence was repeated in other storms in the Midwest on that day. This paper presents results from an analysis of the evolution of the storm using radar data. The analysis concentrates on the impact of the merger of two storm cells on the intensity of the tornado. The Doppler radar analysis shows that there was increased intensity and rotation of the main storm prior to the merger, and a very intense resulting thunderstorm with very strong rotation signatures.