Statistics of equivalent K factor are derived for the mid-Atlantic coast of the United States. These statistics are associated with subrefraction using 3 years of near-continuous line-of-sight link signal measurements at 4.7 GHz in the mid-Atlantic coast of the United States. Probabilities are derived for a family of threshold levels of K factors ranging from 0.6 to 1.0 which are sustained over durations exceeding 1--5 hours. An analytical model is derived that characterizes this family of curves with excellent accuracy. It is, for example, demonstrated that for 6% of the average year the K factor is smaller than 1 for durations greater than 1 hour in the mid-Atlantic coast of the United States. Caveats that should be considered in applying these results are reviewed. Monthly probabilities of K factors statistics reveal that the winter and early spring months dominate. For example, during February of year 1 and December of years 2 and 3 the K factors were smaller than 0.8 for periods exceeding 2 hours at the probabilities of 11.5%, 12.0%, and 11.5%, respectively. This result is consistent with the fact that cold water conditions and warm overlying moist air are more prevalent during the winter season. These conditions represent the correct meteorological ingredients for extreme subrefraction to occur. Annually, the K factor was smaller than 0.8 with durations greater than 1 hour at a probability of 3.2%. ¿ 2001 American Geophysical Union