A special intensive collection of complete flight data for flights above 18,000 ft. MSL furnished detailed data on areas of non-occurrence as well as areas of occurrence of high level turbulence during a selected 5-day period in March 1962. The data were tabulated by 2.5° latitude-longitude “squares.” Frequency distributions and probabilities of turbulence occurrence were computed over individual squares, area configurations, flight elevations, time of day, and for varying values of such meteorological parameters as vertical and horizontal wind shear, location and intensity of jet stream, wind speed, temperature and height of tropopause, Richardson number, flight direction, changes in air temperature, and high clouds. The probability of turbulence occurrence increases fairly uniformly with changes in the value of the vertical wind shear, wind speed, and the Richardson number. The probability of turbulence occurrence responds more erratically with the changes in the values of other parameters, particularly horizontal wind shear. There appears to be no significant relation between the probability of turbulence occurrence and time of day, flight direction, and height and temperature of the tropopause. Presence of high clouds appears to increase the probability of turbulence occurrence.