Why is it difficult to hear when speaking in the presence of strong wind? We say that sound waves require medium for their propagation, but during heavy storms or strong wind we cannot hear sound properly. Even if wind is flowing towards specific direction and we speak in that direction we cannot hear it well. Why is it so?
 A: The process of auditory masking can partially answer the question. A constant wind can present fairly high intensity middle and high frequency noise (pink noise) to the ear. This will mask these frequencies in the speaking voice. These frequencies (>1 kHz) are generally responsible for the "diction" of speech, so you may be able to tell that someone is speaking, but you can't distinguish the words.
Another type of masking occurs with sudden loud noises (like thunder). This auditory input disrupts your ear/brain auditory system enough that you don't process other sounds (like speech) which occur immediately before or after the loud noise.
And, in general, a continuous stream of noise raises the auditory threshhold of all other sounds.  In other words, it's hard to hear your mother talking when you are running the Hoover.
A: Sound waves in air are a series of high and low pressure areas moving through the elastic medium of the air.  If the medium is being compressed and rarefied by other areas of high and low pressure, the integrity of the sound wave may be broken and may become unrecognizable through the background noise of the medium's turbulence.  Here is an explanation of the high and low pressure nature of sound waves in air: http://www.physicsclassroom.com/class/sound/Lesson-1/Sound-is-a-Pressure-Wave.  You may be able to visualize what happens to pressure wave fronts if they become involved with other pressure waves, particularly those carried by strong wind, which generally is not a smooth laminar flow.  
