Which factor contributes to poor visibility during certain atmospheric conditions?

Heavy rain significantly reduces visibility due to the large water droplets that scatter light and create a curtain of water between the observer and the object being viewed. This effect can obscure objects, making it difficult for pilots, including those operating unmanned aircraft, to see the ground, other aircraft, or obstacles clearly. Rain can also create distracting glare under certain conditions, further impacting a pilot's ability to navigate safely.

In addition to the immediate obstruction caused by the precipitation itself, heavy rain can lead to other issues such as reduced contrast and increased likelihood of fog formation afterward, both of which compound poor visibility conditions. Therefore, heavy rain is a primary contributing factor to reduced visibility during certain atmospheric conditions.