More than 150 U.S. Forts daily climate data time series were keypunched by the NOAA Climate Database Modernization Program (CDMP) by summer 2006. Many of these stations provide 10-40 years of data during the period 1850-1895, prior to the onset of previously digitized cooperative observer station records. The temperature and precipitation extreme outliers within these raw station data were subject to rigorous quality control. More than 27,000 temperature and 11,000 precipitation extreme values were examined manually by comparison with optical images of the original forms, and about 30% of these values were changed or set to missing because they were either keyed incorrectly or were keyed correctly but were found to be implausible.

Preliminary time series of indices representing the frequency of conterminous U.S. heat waves, cold waves, and heavy precipitation events display interesting behaviors in the 19th Century. The frequency of 5-day, 1-yr heavy precipitation events has a local maximum around 1870 which is almost as high as modern-day values. Heat wave and cold wave time series defined by 5-day, 1-yr warm and cold event thresholds also contain interannual and interdecadal variance during the late 1800s, displaying interesting linkages between climate variations and extreme weather events. The frequency of heat waves is relatively high prior to the 1890s, which is a local low point. Cold waves, on the other hand, are less frequent during most of the latter half of the 19th Century, leading to the recognition of a broad maximum in cold wave frequency between 1895 and 1920. The final results of this study will be presented, including spatial patterns of trends and composites of event counts for select interannual and interdecadal modes of climate variation.