An Examination of Extreme Climate Events Using 19th Century Daily Data

Daily and at-hour climate observations from forms and manuscripts associated with 19th Century predecessors to the National Weather Service are being keypunched as part of NOAA's Climate Database Modernization Program (CDMP). A subset of stations located for the most part between the Appalachian and Rocky Mountains is currently available for analysis. The frequencies of extreme events at individual stations were identified based on merged time series of co-located 19th and 20th Century daily station observations, and the resulting 1-year, 1-day recurrence interval event thresholds. Analyses of 1-year, 1-day heat wave and cold wave events (1850-1999) and precipitation events (1870-1999) were conducted. Heat wave decadal frequencies appear to have been substantially higher than normal during the 1850s and 1860s, but with less magnitude than the well known 1930s peak. Interestingly, cold wave events were also more common in the 1850s, perhaps indicating dryness in a decade with both warm and cold extremes. Another local peak in cold wave frequency occurred during the 1880s. Finally, 1-year, 1-day precipitation event frequencies were lower in the 1880s and early 1890s than in the late 1890s. This finding suggests that the late 19th Century peak in heavy precipitation events may be an isolated feature in a record that is generally of lower frequency from the 1870s until increases seen in recent decades. These preliminary findings are intriguing, but are not complete. Work on improved homogenization and extreme outlier quality control is currently underway, and will be discussed in this presentation.