Are there any web sites that provide the standard deviations for the daily average highs and lows for RDU (or preferably for Chapel Hill)?

MIKE MOSS SAYS:       Kent,    You can find some listings of average high and low temperatures, along with the applicable standard deviations, at the Southeast Regional Climate Center site. As you might expect, the standard deviation for low and high temperatures in our area is much larger (around 10-12 degrees) in the winter when strong midlatitude low and high pressure systems are passing through the region than in midsummer (around 3-6 degrees) when we are dominated by the Bermuda high and most frontal boundaries remain well to our north. Here is a good starting point for you to work from:

http://www.sercc.com/climateinfo/historical/historical_nc.html

Just pick a station and look for the "Daily Tabular Data" links.