I haven't read all the responses, but you hear sounds differently on different days due to atmospheric inversions or ducting. Wind is important, but the vertical structure of the atmosphere at any particular time is critical. Atmospheric ducts are regularly created by strong inversions -- which are most common in winter and at night. The boundary of the inversion (the edges of the duct layer) acts as a reflector of sound because of the air density difference -- causing refraction -- and sound shadows. Depending on the height of the duct and the frequency of the sound, the "sound" can travel for miles. Even hundreds of years ago, when canons were commonly used, people noticed that sometimes nearby people barely heard the sound, yet folks miles away heard the canons very clearly. In other words, there can be dead sound spaces (shadows) between the sound areas during strong atmospheric ducting. Any good sounding (or raob) program will identify these inversions -- or ducting layers. Here is an excellent article on this subject ...
Refraction of Sound Waves & Acoustic Shadows Explained