The relationship between the total precipitable water in the atmosphere and surface absolute humidity has been examined for more than 1500 upper level soundings. Total precipitable water and surface absolute humidity were computed for all of the upper level soundings made in 1970 at San Nicolas Island, Point Mugu, and China Lake, Calif. These stations, separated by less than 200 nil, are representative of a maritime, a coastal, and a desert environment, respectively. The monthly correlation coefficients, ranging from −0.29 to +0.83, indicate that a direct but widely variable relationship exists between the total precipitable water and surface absolute humidity; however, these results also demonstrate that estimates of total precipitable water from surface humidity measurements are not valid. Abstract The relationship between the total precipitable water in the atmosphere and surface absolute humidity has been examined for more than 1500 upper level soundings. Total precipitable water and surface absolute humidity were computed for all of the upper level soundings made in 1970 at San Nicolas Island, Point Mugu, and China Lake, Calif. These stations, separated by less than 200 nil, are representative of a maritime, a coastal, and a desert environment, respectively. The monthly correlation coefficients, ranging from −0.29 to +0.83, indicate that a direct but widely variable relationship exists between the total precipitable water and surface absolute humidity; however, these results also demonstrate that estimates of total precipitable water from surface humidity measurements are not valid.