Which weather phenomenon can severely affect VFR navigation?

Low visibility is a significant weather phenomenon that can severely impact Visual Flight Rules (VFR) navigation. In VFR, pilots are required to maintain visual reference with the ground, and low visibility conditions make it challenging or impossible to see terrain, obstacles, and navigational aids. This situation can arise from several factors such as fog, mist, rain, or snow, all of which can reduce a pilot’s ability to see clearly and navigate safely.

Although high winds, temperature inversions, and heavy precipitation can also affect flight operations, they do not pose the same immediate and grave threat to a pilot's ability to navigate visually. High winds can create turbulence and might complicate landing and takeoff but do not inherently affect visibility. Temperature inversions can impact flying conditions, often leading to cloud cover and fog, but the direct effect is not as immediate as visibility issues. Heavy precipitation can decrease visibility, but it is not always an absolute barrier to navigational capability, depending on how dense it is. Therefore, low visibility stands out as the predominant factor in compromising VFR navigation.