An overview of environmental conditions and forecast implications of the 3May 1999 tornado outbreak

An overview of conditions associated with the Oklahoma- Kansas tornado outb reak of 3 May 1999 is presented, with emphasis on the evolution of environm ental and supercellular characteristics most relevant to the prediction of violent tornado episodes. This examination provides a unique perspective of the event by combining analyses of remote observational data and numerical guidance with direct observations of the event in the field by forecasters and other observers. The 3 May 1999 outbreak included two prolific superce lls that produced several violent tornadoes, with ambient parameters compar able to those of past tornado outbreaks in the southern and central Great P lains. However, not all aspects leading to the evening of 3 May unambiguous ly favored a major tornado outbreak. The problems that faced operational fo recasters at the Storm Prediction Center are discussed in the context of th is outbreak, including environmental shear and instability, subtle processe s contributing to convective initiation, the roles of preexisting boundarie s, and storm- relative flow. This examination reveals several specific aspe cts where conceptual models are deficient and/ or additional research is wa rranted.