Why do VHF signal strengths sometimes vary greatly when the antenna is moved only a few feet?

When VHF signals travel, they often bounce off buildings, hills, and other terrain, creating multiple paths from the transmitter to the receiver. Because these paths are different lengths, the signals arrive at slightly different times. If the signals arrive in phase, they reinforce each other and the signal is strong. If they arrive out of phase, they cancel each other out, creating a dead spot. Because VHF wavelengths are relatively short (around 2 meters for the 144 MHz band), moving an antenna just a few feet can drastically change these phase relationships, turning a weak signal into a strong one. Distractors like Doppler shift and water vapor concentration are incorrect because they do not cause sudden, localized changes in signal strength over just a few feet of stationary distance.