Estimating the Probability of Clear Lines-of-Sight from Sunshine and Cloud Cover Observations

Observations of hourly sunshine, angular elevation of the sun above the horizon, cloud cover, and a three-dimensional cloud model, were utilized to derive a set of cloud width, thickness, and spacing values for estimating the probability of clear lines-of-sight from any angle. Data for Tampa, Florida, were used to illustrate cloud parameters that satisfy the cloud model. The observed “typical” values of cloud width and spacing fit the model very well. The computed average earth cover was much less than the observed average cloud cover because the observers did not see all the spaces between clouds.