Quantifying the non-Gaussianity of wintertime daily maximum and minimum temperatures in the southeast United States

Understanding the statistical distribution and probabilities of extremes in daily winter temperatures is of practical interest to the realms of ecology, agriculture and utilities planning. This is particularly true for regions such as the southeast United States where winter hard freezes are a relatively rare and potentially catastrophic occurrence. The relationship between the El Nino – Southern Oscillation (ENSO) and the average winter temperatures in the southeast United States is well known, with El Nino winters on average cooler than La Nina winters. An additional large-scale control for the wintertime temperatures in this region is provided by the Atlantic Oscillation (AO), with a negative AO phase being associated with colder winters compared to the positive AO phase. A limited number of studies examine how ENSO and/or AO affect United States' daily temperature averages. The details of the effect of ENSO or AO on the higher order statistics for wintertime daily minimum and maximum temperatures have not been clearly documented.

We use a 50-year record of quality-controlled observations collected from 272 National Weather Serivce's (NWS) Cooperative Observing Network (COOP) stations throughout Florida, Georgia, Alabama, and South and North Carolina to calculate the first four statistical moments of minimum and maximum daily temperature distributions. We find that, over the Southeast, winter minimum temperatures have higher variability than maximum temperatures, and La Nina winters have greater variability of both minimum and maximum temperatures. We also find that, with the exception of Florida's peninsula, minimum temperatures are positively skewed, while maximum temperatures are negatively skewed. Stations in peninsular Florida exhibit negative skewness for both maximum and minimum temperatures. During the relatively warmer winters associated with either a La Nina or a positive phase of the AO, negative skewnesses are exacerbated and positive skewnesses are reduced. To a lesser extent, the converse is true of El Nino and the negative phase of AO. ENSO and AO are also shown to have a statistically significant effect on the change of kurtosis of daily maximum and minimum temperatures throughout the domain.