Question

Velocity of sound increases on cloudy day. Why?

Answer 1

speed of sound in gases is given by the formula\[\sqrt{\gamma RT/M}\] where, gamma is the adiabatic constant of the gas, R is the universal gas constant and M is the average molecular mass of the gas in which sound is travelling
when the weather is cloudy, the air is humid and thus, contains some water vapor
it has been seen theoretically and also experimentally that the average molecular mass of humid air is less than that of the dry air and there is not much difference between the adiabatic constants of dry and humid air at the same temperature.
Thus, as the average molecular mass of the air in cloudy weather is lower than that of the avg. molecular mass of normal air, the speed of sound increases on a cloudy day
hope this helps you!