El cielo está nublado y gris, y hace frío. Hace mal tiempo.
Explanation:
El cielo está nublado y gris, y hace frío. Hace mal tiempo. This means there's <u>bad weather</u>. Nublado is an adjective that means cloudy. Gris means gray. The expression "hace frío" means it's cold. The whole phrase in English is: the sky is cloudy and gray and it's cold.
"Hace buen tiempo", is the opposite: good weather. The sky should be clear and sunny. In Spanish it would be "el cielo está despejado y soleado".