Cloud cover
When a target is marked by a designator, the beam is invisible and does not shine continuously. Instead, a series of coded pulses of laser light are fired. These signals bounce off the target into the sky, where they are detected by the seeker on the laser-guided munition, which steers itself towards the centre of the reflected signal. Unless the people being targeted possess laser detection equipment or can hear aircraft overhead, it is extremely difficult for them to determine whether they are being marked. Laser designators work best in clear atmospheric conditions. Cloud cover, rain or smoke can make reliable designation of targets difficult or impossible unless a simulation is accessible through available ground data.