An example forward scatter sensor comprises: a transmitter to emit a light sheet; a receiver to observe light scattered from particles that fall through a measurement volume; and a control entity comprising an analyzer to record a measurement signal descriptive of intensity of light captured by the receiver as a function of time and to: carry out a precipitation analysis on basis of a time segment of the measurement signal; carry out a verification of analysis performance based on magnitudes of first peaks of at least one identified double peak and on respective residence times for said at least one identified double peak; and invoke a predefined maintenance action responsive to said verification indicating a threshold-exceeding difference between respective size estimates derived based on magnitudes of the first peak of said at least one identified double peak and based on residence times of said at least one identified double peak.