NOAA ThreadEx Long-term Station Extremes for America
ThreadEx is a data set of extreme daily temperature and precipitation values for 270 locations in the United States. For each day of the year at each station, ThreadEx provides the top 3 record high and low daily maximum temperatures, the top 3 record high and low daily minimum temperatures, the top 3 daily precipitation totals, along with the years the records were set for the date. Many of the time series are available back to the 1800s AD. This archive was developed for the express purpose of conveying general climate perspectives information. It is not appropriate for climate research.
Stitches together data from multiple sources to create long time series of extreme temperatures and precipitation amounts for each day of the year
Limited online documentation (more to be added here when available)
The 'threading' of data from nearby stations along with no adjustments for changing location and instrumentation makes it unsuitable for (say) climate change research.