A method of operating an optical icing conditions sensor includes transmitting a first light beam with a first transmitter and a second light beam with a second transmitter, thereby illuminating two illumination volumes. A first receiver receives the first light beam. A second receiver receives the second light beam. A controller measures the intensity of light received by the first and second receivers. The controller compares the intensities to threshold values and determines if either intensity is greater than the threshold values. The controller determines a cloud is present if either intensity is greater than the threshold values. The controller calculates a ratio of the intensities if a cloud is present. The controller determines, using the ratio, whether the cloud contains liquid water droplets, ice crystals, or a mixture of liquid water droplets and ice crystals.