The Lambert St. Louis observation station has a 149-year (1874 – 2022) period of record, inclusive of missing data years between 1930 and 1936. The Columbia, MO station has a 133-year (1890-2022) period of record. At the St. Louis station the 30 year running mean of annual precipitation has increased about 20% from about 34 inches to about 42 inches between 1980 and 2022. A similar trend is observable at the Columbia station, although not as pronounced and with a higher degree of variability. In addition to monthly and seasonal relationships, extreme events, such as the extreme wet event that occurred on July 26, 2022, or protracted dry spells as occurred in Spring/Summer of 2023, may influence these long term annual precipitation trends. The goal of this investigation is to identify the extent to which a seasonal component, and perhaps even a monthly component contributes to this observed trend in annual precipitation. In addition, this investigation assesses the contribution of trends in extreme precipitation events influence annual precipitation trends. This information may be useful to water supply officials, wastewater and stormwater utilities, and emergency managers for both flood events and for drought response and mitigation. It is envisioned that this research can be expanded to investigate and evaluate rainfall trends along comparable lines of latitude and longitude to identify if there is an observable geographic trend (within the same Midwest climate regime) as well as a temporal trend.
