Abstract:
A tornado outbreak of 44 tornadoes, five of which were F4s, killed 58 people and injured 1113 along a narrow axis that included parts of Illinois, Michigan, Missouri, Indiana, and Iowa on 21 April 1967. To the author’s knowledge, no formal analysis has been conducted on this historic case, making it a good event to examine so that we may better understand the causes behind the confinement of the storms to a narrow band. This study used synoptic and mesoscale analyses, along with digital archived data, hand written surface observations, and output from a re-run Eta model to recreate the conditions present on that day. These tools show that several components favorable for severe weather were present as a fast moving short wave trough moved through the area and helped initiate the numerous storms that formed during the outbreak. Not only was the short wave trough moving rapidly, but the environmental conditions ahead of the system evolved quickly. With the combination of the fast moving system, and the rapid evolution of the environment, it was difficult to predict the extent of the outbreak and its extension into Michigan. This aspect of the outbreak made preparation difficult and should a similar outbreak occur in the future, difficulties could again be faced.