Assessing of the influence of wind direction and velocity and the angle of slope on unitary value of rainfall and comparison of this value with parameters obtained from ombrometrs showed that measured values of rain intensity obtained with the use of horizontally located measuring level of ombrometrs differ from potential intensity value (in a plane perpendicular to rainfall direction). To determine potential rain intensity additional monitoring or rainfall angle is necessary. Calculated rain intensity in a plane of inchined slope differ significantly from potential intensity and those measured in ombrometrs. This differentiation increases with slope increase. When calculating rain intensity plane deviated from perpendicular, it is also significant direction of rainfall.