American Meteorological Society Certification (AMS) Practice 2025 - Free Practice Questions and Study Guide

Fog is defined in meteorological terms as a thick cloud of tiny water droplets near the ground. This definition emphasizes that fog consists of liquid water droplets suspended in the air, which causes reduced visibility. The presence of these tiny droplets means that fog forms when the air near the ground cools and can no longer hold all of the moisture it contains, leading to condensation.

This definition is critical for understanding various weather phenomena, as fog significantly affects visibility and can lead to hazardous conditions for transport and outdoor activities. Other options describe different meteorological phenomena; for instance, a thick cloud of water vapor is more representative of larger clouds in the atmosphere, while a layer of ice crystals would describe freezing fog or frost, which has different implications. Rainfall at low temperatures pertains to other weather conditions and does not accurately capture the characteristics of fog.