Setting and mood. Weather is a part of your setting and you can use it to enhance the mood of your scene.
Bright sunshine usually makes the reader think of happy times and dark cloudy days or storms could reflect a brooding character or story line. Don’t describe just how it looks, use all the senses. Is the air thick with humidity, is the rain cold on your skin, or how does it smell after a rain. Taste the rain drop, describe the scent of leaves as they are raked or dust on a dry country road that catches in your throat.
How do you use weather for settings?