Mesoscale Association of a Low-level Jet Stream with a Squall-Line—Cold-Front Situation

J. R. Gerhardt The University of Texas

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Abstract

Wind and temperatures data taken at twelve levels on a television tower near Dallas, Tex., are examined during a squall-line—cold-front situation occurring during the morning hours of 8 May 1961. The observations, supplemented by Fort Worth pibal and radiosonde data, illustrate the presence of a large scale low-level jet stream in the southwesterly flow in advance of the squall line, a wind maximum and marked cooling associated with a thunderstorm outdraft and a separate, smaller scale jet stream which existed within a mesoscale high pressure area between the squall line and the cold front. This mesoscale high, of the type studied by Fujita, is produced by sub-cloud precipitation evaporation. Detailed vertical soundings show the extent of the corresponding subsidence inversion and the resulting effect on the wind speed profile.

Abstract

Wind and temperatures data taken at twelve levels on a television tower near Dallas, Tex., are examined during a squall-line—cold-front situation occurring during the morning hours of 8 May 1961. The observations, supplemented by Fort Worth pibal and radiosonde data, illustrate the presence of a large scale low-level jet stream in the southwesterly flow in advance of the squall line, a wind maximum and marked cooling associated with a thunderstorm outdraft and a separate, smaller scale jet stream which existed within a mesoscale high pressure area between the squall line and the cold front. This mesoscale high, of the type studied by Fujita, is produced by sub-cloud precipitation evaporation. Detailed vertical soundings show the extent of the corresponding subsidence inversion and the resulting effect on the wind speed profile.

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