What is a primary hazardous effect of a thunderstorm on visibility?

Thunderstorms can significantly impact visibility primarily through the heavy rains and intense precipitation they produce. When a thunderstorm occurs, it often brings about a sudden and drastic reduction in visibility due to the downpour, which can obscure road signs, traffic signals, and other visual references that drivers rely on for safe navigation. This limited visibility can create hazardous driving conditions, increase the risk of accidents, and complicate outdoor activities.

While fog formation can also reduce visibility, it is a separate weather phenomenon and not a direct result of thunderstorms. Enhancements to visibility or extreme heat are not typical effects associated with thunderstorms. Therefore, the correct choice reflects the direct impact thunderstorms have on visibility through heavy precipitation.