The phrase "became sunny" suggests a change in weather from cloudy or overcast conditions to clear and bright skies. Antonyms for this term might include words like "became cloudy," "turned stormy," or "darkened." These phrases describe the opposite of the original meaning and imply a shift towards less favorable or pleasant weather conditions. Other antonyms could include terms such as "gloomy," "dim," or "dull," which convey a sense of darkness or lack of light. Overall, antonyms for "became sunny" emphasize the contrast between light and dark, and suggest a shift away from warmth and brightness towards coolness and darkness.