Which type of weather event can cause visibility to drop in a short duration, but may not qualify as precipitation?

Fog is a weather phenomenon that can significantly reduce visibility within a short time frame without involving precipitation in the traditional sense. Unlike rain or drizzle, which involve the falling of water droplets from clouds, fog consists of tiny water droplets suspended in the air close to the ground. This can lead to a sharp drop in visibility because it creates a blanket of moisture that scatters light, making it difficult to see clearly.

Fog can occur when warm, moist air cools to its dew point, and can form rapidly under certain conditions, leading to almost instantaneous reductions in visibility. Because fog does not entail the falling of water from clouds to the ground, it does not qualify as precipitation, which further distinguishes it from the other weather events listed. Heavy rain, snowflakes, and drizzle all involve precipitation and result from the condensation of atmospheric moisture that falls from clouds, thereby increasing visibility issues but solely within the context of precipitation.