historical minimum temperatures for RDU
Hopefully everyone is enjoying their Holiday season.
The USDA Zone assignments are based on quite extensive processing of temperature data that involves location pooling and averaging so they lack precise details as to what minimal temperatures can be expected in a given year and how much they would vary from year to year, so an inquiring mind may be interested in looking at the actual historical data.
Even with the many excellent online weather resources, in particular from the NC State Climate Office and National Weather Service, we had troubles finding records of long-term per month historical minima. Most tools show either absolute minima for a given calendar day or short term historical records. However, we recently discovered that the National Climatic Data Center, another unit of NOAA, has long-term monthly summary data available for download.
We used such data for the RDU airport to generate the attached graph that gives more detail about how the actual monthly minimal (as well as maximal) temperatures varied within the last 20 years. (Average min, mean, and max plotted in light lines).