The optimum time and space distribution of upper-air observations is considered in connection with the detection and prediction of instability lines—a mesoscale phenomenon. It is shown that the optimum spacing of observational stations is not only a function of the scale of the phenomena to be detected but of observational and analytical errors as well. When these errors are considered the optimum network spacing can be determined with regard to the dimensions of the atmospheric feature requiring detection. Because actual data are lacking, inferences concerning the maximum time and space distribution of upper-air sounding stations suitable for the detection of instability lines are drawn from a theoretical atmospheric model.