| description abstract | Composite charts of height (or sea level pressure), temperature, and dew point were prepared for the surface, 850-, 700-, and 500-mb. levels for tornado occurrences in 6 different areas in the United States. Cases selected for inclusion in these composite charts were mostly based upon the occurrence of 3 or more tornadoes within any one of the 6 areas during a 12-hour period. The number of cases ranged from 17 to 66 in any one area with a total of 229 cases. These charts present a mean picture of synoptic conditions from 0 to 12 hours before the outbreak of tornadoes for each of the 6 areas. In spite of seasonal and geographical differences in data, the similarity of patterns is striking. | |
