The Jet Chart

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.