Vertical Structure of Thunderstorm Outflows

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Abstract
Cold air outflow from thunderstorms has been observed from a multi-level 461 m tower in central Oklahoma. Four life-cycle stages are determined from 20 outflows sampled. Each outflow is affected by the behavior and character of the parent thunderstorm and by the flow and stratification in both the warm ambient air and the cold outflow air. This produces much variation from case to case and makes difficult the description of a representative outflow model. However, cases believed to depict each of the outflow stages are chosen and discussed in detail. The study is confined to the tower layer depth and concentrates on the characteristics of the outflow's leading edge. Outflow origin is not discussed. The leading edge of the outflow is characterized by strong shears in horizontal and vertical winds. Updrafts, which occur in a 1.5 km wide band ahead of the outflow, often exceed 6 m s−1. Maximum low-level horizontal wind gusts are found to be directly related to the translational speed of the front. F... Abstract Cold air outflow from thunderstorms has been observed from a multi-level 461 m tower in central Oklahoma. Four life-cycle stages are determined from 20 outflows sampled. Each outflow is affected by the behavior and character of the parent thunderstorm and by the flow and stratification in both the warm ambient air and the cold outflow air. This produces much variation from case to case and makes difficult the description of a representative outflow model. However, cases believed to depict each of the outflow stages are chosen and discussed in detail. The study is confined to the tower layer depth and concentrates on the characteristics of the outflow's leading edge. Outflow origin is not discussed. The leading edge of the outflow is characterized by strong shears in horizontal and vertical winds. Updrafts, which occur in a 1.5 km wide band ahead of the outflow, often exceed 6 m s−1. Maximum low-level horizontal wind gusts are found to be directly related to the translational speed of the front. F...

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