When water droplets are observed falling from the sky, what phrase is correct?

The phrase "It's raining" is correct when water droplets are seen falling from the sky because rainfall specifically refers to liquid water droplets that descend from clouds. This is a common meteorological phenomenon that occurs when humidity in the atmosphere condenses into water droplets, which grow heavy enough to fall to the ground due to gravity. The occurrence of noticeable water droplets indicates that the atmospheric conditions are conducive to precipitation, thus accurately describing a rain event.

The other options describe different weather conditions that do not correlate with the presence of falling water. Windy conditions may or may not accompany rain, snowfall indicates the presence of ice crystals rather than liquid droplets, and sunny weather typically implies clear skies with no precipitation. Thus, the observation of water droplets clearly aligns with the phenomenon of rain.