The antonyms for the phrase "be overcast" can be "be sunny," "be clear," "be bright," and "be cloudless." These words describe the opposite of a gloomy or cloudy day, and instead signify a bright and clear sky. While an overcast day may bring feelings of dreariness and dampness, a sunny day can lift one's spirits and make the world seem more vibrant. The contrast between these two states of weather can signify a change in mood or atmosphere, with a bright day eliciting feelings of joy and optimism.