In a study of the 200-mb Height Chart and associated jet to determine their usefulness in tornado forecasting, a consistent phenomenon was observed, namely, that the majority of tornadoes investigated occurred along or near the −60°C isotherm at 200-mb. More precisely, the western and southern portions of the −60°C isotherm of the cold “pool” it circumscribed were the favored area. The jet at 200-mb in most cases delineated that portion of the −60°C isotherm under which tornadoes occurred. Further, certain consistencies appeared on the tropopause chart that might be related with tornado occurrence.

In a previous paper [5] the authors have indicated the observed relationship between the jet at 200 mb, the −60C isotherm at 200 mb and tornado occurrences. The location of this jet has become important in severe local storm forecasting procedures. Often, the lack of a band of strong winds at 500 mb, especially during the summer months, made this level ineffective as an aid in locating the jet some height above. The 20-mb data are not transmitted until more than six hours after time of observation; thus, the formulation of a chart which is not a constant-pressure chart and called by SELS “The JET CHART” was conceived to remedy this situation. The preparation, analysis, and use of this chart in severe local weather forecasting are set forth here.

Aircraft have been guided with the aid of radar data to measure turbulence in thunderstorm areas. Although turbulence is frequently encountered in areas containing highly reflective and sharp-edged echoes, no unique correspondence has been discovered between single-echo parameters and collocated within-storm turbulence. A theory embracing some of the time-dependent relationships between fields of wind and precipitation suggests that the correspondence between instantaneous distributions of radar echoes and turbulence is statistical rather than precise. Statistical bases for study of radar echo-turbulence relationships are outlined.

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