The term "become overcast" refers to the situation when clouds start gathering and the sky turns grey, signaling an impending change in the weather. There are several synonyms for this phrase, including "get cloudy," "turn dark," "cloud over," "obscure," "shadow," and "veil." In addition, the phrase "get gloomy" can also be used to describe this phenomenon. When describing a sudden change in the weather, people may also use the phrases "storm clouds gathering,""threatening clouds," and "skies darkening." No matter which synonym is used, the purpose is to convey the message that the weather is about to change and potentially become stormy or rainy.