What Daily Area Averages of Temperature and Precipitation Reveal about the Climate of the Contiguous United States

What was the hottest day for the contiguous United States (ConUS) as a whole during The past 30 years? What fraction of the ConUS is covered by precipitation on the typical January day? These and other tantalizing questions about the climate of the ConUS as a whole will be answered during this presentation. Answers will be based on analyses of a collection of daily gridded and area-averaged precipitation and temperature for the contiguous United States that has recently been developed at the National Centers for Environmental Information (NCEI). This product, called NClimDiv-Daily, will extend back to at least 1981, will be updated daily once it becomes operational.

The area averages are generated by first interpolating observations from the Global Historical Climatology Network - Daily dataset to a nominal 5-km grid and then averaging the gridpoint values. The Australian National University implementation of thin-plate smoothing splines (ANUSPLIN) is used as an interpolator, taking into account coastal proximity and topography. Care is taken to minimize spatial variations in the begin/end times of the 24-hour observational day, to reduce the impact of changes in instrumentation and observing practice on the temporal homogeneity within the product, and to ensure consistency with the already operational monthly NClimDiv product.

While caution should be used when looking at trends in extremes at individual grid points, the product is useful for identifying events that are unusual in terms of a combination of aerial extent, duration, and relative magnitude, as will be demonstrated in this presentation.