The High Speed Updraft—The Key to the Severe Thunderstorm

Abstract

A model of the motion within a severe storm with some rainfall kinematics is developed from simple hydrodynamic concepts of flow. Based on measured data and descriptive analyses of storms with sufficient data to permit the assumption of a steady state, this paper supports the statement that the large, strong and erect updraft is the single guiding most essential element of the steady-state storm. A mathematical formulation of the flow in this open single-celled storm is made using complex potentials to represent each of five differing layers of the environment. The resulting functional forms are dependent on the form, size and maximum values of the vertical motion, and to a lesser extent on the parameterized heights where significant changes occur in the environment. A modification of Kessler's rainfall kinematics is made to apply to the one-dimensional portion of the flow model. The simplified case of the rainfall kinematics results in the oftentime associated radar echoes (e.g., the echo free vault), while computed values of precipitation compare favorably with record rainfall rates. The internal consistency of the model and the mathematical formulation in parameterized form allow quantitative considerations to be made from presently measurable airflow data. Therefore, making a prognostic model from this essentially diagnostic model should be the next undertaking.