Specific cases are cited which show the existence of a clear-cut frontal zone at the 500-mb level. The relationship of this frontal zone to the location of the jet stream and to the formation of surface disturbances can be used as a valuable tool for forecasting. The value of the data received from weather reconnaissance flights is emphasized and recommendations for improving these flights are given.
*Present address: Academy of Finland, Helsinki, Finland.
†This paper was prepared under a research contract between the Office of Naval Research and The University of Chicago.
