Expanding the historical 'outbreak' climatology in the U.S. between 1880 to 1989

<p>Tornado outbreak climatology is constantly evolving. Modern research highlights the current trends in tornado outbreak activity in the United States using the Storm Prediction Center’s tornado database, which dates back to 1950. Here, digitized tornado records over the period 1880–1989 are used to create a historical climatology of tornado outbreaks. In total, 462 unique clusters are identified encompassing more that 4,500 tornadoes. The spatial and temporal analysis of these clusters highlight trends that are consistent with current research which indicates similar trends in the modern record. The spatial distribution of the historical clusters follows an L-shaped pattern, with tornadoes extending from Iowa to Oklahoma to Georgia consistent with modern tornado outbreak climatology. The historical tornado clusters show significant upward trends in the total number of clusters, tornadoes, and casualties by decade which is seen in the modern record as well. Additionally, tornado clusters show similar upward trends seasonally and diurnally. Most clusters occur in March, April, and May and start in the early afternoon hours. The results of this research support the current trends detected in the modern tornado record.  Future research will look to combine historical and modern tornado records to develop a more complete climatology of clusters since 1880. </p>