Minecraft wiki entry for Daylight_detector, associated text: Using a redstone clock that is synchronized with the Minecraft day that is broken up into segments according to the daylight sensor power output schedule, it is possible to use many daylight sensors to build a rainstorm and thunderstorm detector. Use a comparator to reduce the redstone clock's signal strength to below that of the daylight sensor's clear day output. Wire this into the side of another comparator that has a daylight detector wired to the back. The wire coming out of the end of the comparator deactivates whenever there is a storm. Using this you can detect both rain and thunderstorms using two lines with adequate comparator sensitivity. Using this you can signal an alarm whenever there is a storm, count the number of storms, count the duration of the storms using another clock and some type of memory, and even all three. Note, however, that if the chunk is unloaded for any length of time, the redstone clock falls out of sync with the daylight sensors.