What is already known:
What this study adds:
This study evaluates a 180-year climatology for the period 1836–2015 of severe weather environments in the United States using 20th Century Reanalysis version 3. Various composite thresholds are utilized to establish severe weather environments and the number of days of these severe weather environments (NDSEV) calculated for each year. Regional comparisons demonstrate trends of frequency of severe storm environments for various geographic regions of the U.S. Annual cycles are analyzed to explore seasonality of severe weather. Compared to the mid 19th century, NDSEV in the Southeast has increased by 15.7 days and decreased in the Northern Plains by 15.5 days. The beginning of severe weather season has moved over a month earlier in the year. Additionally, potential inconsistencies are in the reanalysis are subjectively identified, specifically in evaluated magnitudes of severe storm parameters.