Antonyms for the phrase "becomes sunny" would describe changes in weather that are not associated with bright, clear skies. Some potential antonyms could include "cloudy," "overcast," "rainy," "stormy," or "foggy." Each of these terms indicates a shift away from sunny conditions, whether caused by cloud cover, precipitation, or other weather phenomena. In contrast to sunny weather, these conditions often make outdoor activities more difficult or unpleasant, such as causing slippery or muddy conditions, reduced visibility, or wet clothing. Despite their negative connotations, these weather patterns serve valuable purposes in regulating the earth's climate and supporting a wide variety of organisms.