The Prophet Elias, not surprisingly given his profession, was a shrewd forecaster. At the height of a prolonged drought in Israel he told Ahab: "Go up and eat and drink, for there is the sound of the abundance of rain". And sure enough, the Book of Kings tells us that in a few hours "the heavens grew dark with clouds and wind, and there fell a great rain", whereupon the eccentric Elias "girded up his loins, and ran before Ahab, till he came to Jezrahel".
The passage suggests that Elias subscribed to the widespread belief that sound carries particularly well in the few hours immediately prior to the onset of general rain. It is also reflected in the old proverb:
Sound travelling far and wide
A stormy day will betide.
Both Elias and the proverb have a point. In the first place, the sky becomes increasingly cloudier with the approach of rain, and so the ground is protected from the direct heat of the sun. Vertical convective currents in the atmosphere, usually triggered by the heating of the ground, are therefore weak or non-existent; this in turn reduces turbulence in the air, which in more sunny conditions tends to make sound dissipate. In addition, the approach of rain also brings about an increase in the humidity; humid air, by definition, has a high water vapour content, and this improves its sound-carrying capacity.
A third factor concerns the thermal structure of the atmosphere. On a sunny day, the air temperature near the ground is high, but it falls sharply with height in the first few tens of feet above the surface. This has the effect of causing sound waves originating near the ground to bend upwards as they spread out from their source making sounds from some distance away less audible than they would otherwise be.
Conversely, on clear starry nights as the Earth loses heat by radiation, the air temperature near the ground is usually much lower than that some distance up above, and temperature rises with height. This has the opposite effect, diverting sound waves that might originally have headed upwards, back again in the direction of the ground making distant noises on a clear night more audible than they really ought to be.
However, with the approach of rain, even during the day, the atmosphere normally assumes what meteorologists call a "stable" condition: the usual daytime decrease in temperature with height is diminished, or perhaps even reversed. This traps the sound waves near to the surface of the Earth, allowing them to spread horizontally for a comparatively long distance before being attenuated to inaudibility.